With the MCU turning the page into an entirely new chapter with the dawn of Phase Four, some of the surviving heroes from Phase One deserve a proper and fitting sendoff. Many of the original Avengers met their end in Avengers: Endgame, which was a culmination of the MCU's first three phases, a storyline that Kevin Feige has taken to calling "The Infinity Saga." Familiar faces like Black Widow (Scarlett Johansson) and Iron Man (Robert Downey Jr.) met their demise while stopping the Mad Titan Thanos (Josh Brolin) from fulfilling his destiny and completing the Snap a second time, while Captain America (Chris Evans) decided to leave the Captain America shield in capable hands and return to the past to be reunited with his greatest love.
Fortunately for the universe at large, there are more than enough new heroes to pick up the slack. Characters introduced in Phases Two and Three will be taking on much larger roles this time around, with Sam Wilson (Anthony Mackie) set to become the new Captain America, and heroes like Captain Marvel (Brie Larson) and Doctor Strange (Benedict Cumberbatch) protecting Earth from threats both intergalactic and interdimensional. Phase Four will also debut several brand new characters as well, such as the nigh-immortal Eternals, Marvel's resident master of martial arts Shang-Chi, and various heroes who will debut in their own Disney+ shows.
As more new heroes are introduced to carry the torch, the MCU will soon have to retire even more of their original characters, as the actors probably want to find proper ways to bring their roles full circle. Luckily for them, there's more than enough context within the movies and within the comics for each surviving Phase One hero to have a satisfying ending.
Nick Fury
Samuel L. Jackson's stern and pragmatic Nick Fury has been making the tough decisions and encouraging the Avengers since his first appearance in Iron Man 2, and it doesn't seem as if he's stopping any time soon. Captain Marvel took viewers back to the '90s in order to see a younger version of Fury encounter the shapeshifting Skrulls for the first time, and Spider-Man: Far From Home turned around and revealed that the real Fury is currently off-world, working on some sort of project with the Skrulls. Fan speculation points towards their joint project being the formation of S.W.O.R.D., an intergalactic defense agency not unlike Earth's own S.H.I.E.L.D. Having Fury lead this new organization would be a perfect progression of his character, but it could also provide an exciting way to send him off while opening the door to a new actor playing the character.
In the comics, Fury has frequently employed the use of LMDs, a.k.a. Life Model Decoys, which are synthetic androids created with the mental and physical capabilities of their original likeness. Several characters have been revealed to be LMDs in the comics, including Dum Dum Dugan, Tony Stark, and even Fury himself. LMD technology has already been referenced in Marvel's Agents of S.H.I.E.L.D.; what if Nick Fury were secretly using LMDs to create perfect androids of himself to carry on leadership of S.W.O.R.D. in the aftermath of his potential death. A film like Captain Marvel 2 could finally kill off the original Fury once and for all, only to pass the character off to a younger actor through the usage of an LMD trained to think that they are the real Nick Fury. This would open the door to many new adventures and potentially even a film or Disney+ series, while at the same time providing a clever ending for Samuel L. Jackson's version of the character.
War Machine
Colonel James Rhodes (Don Cheadle) has always been just as much of a hero as his best friend Tony Stark, so it only seems natural that he would continue to be one after Stark's death. Fans and audiences have speculated alike whether or not the MCU would introduce an Iron Man replacement, and while a subsection of fans would love to see Harley Keener (Ty Simpkins) from Iron Man 3 take on the role, the most natural and fitting replacement would of course be Riri Williams, the young scientific prodigy who becomes Ironheart in the comics. Her introduction into the MCU could provide a compelling storyline for Rhodey, as he could take on a mentorship role towards her after the creation of her first suit of armor goes viral. As someone who has worked closely with Tony, Rhodey is the perfect character to train and push Riri, as he would recognize that same spark of creativity and ingenuity within her that birthed the original Iron Man.
Another fitting story direction for Rhodey would be him eventually becoming the head of S.H.I.E.L.D. His time in the military, coupled with his experiences dealing with the Avengers and the Sokovia Accords, would make him the perfect leader for such a secretive counter-intelligence organization. Rhodey has seen firsthand the cost of superhuman interventionism, and it's this expertise that would allow him to work with the heroes in a way that's conducive for them and the world at large.
Hawkeye
Clint Barton (Jeremy Renner) has always been a character that has toed the line of morality in the MCU, although not always intentionally. His first real named appearance in The Avengers turned him into a brainwashed soldier for Loki, and although he embraces his position as an Avenger in Age of Ultron, Civil War labels him an international terrorist for working with Captain America, and Avengers: Endgame features him in the Ronin persona working through his internalized rage and helplessness by slaughtering international criminals. Couple this with the character's vague background as an assassin, and Clint has a lot of guilt and misgivings to work towards fixing. Luckily, the upcoming Hawkeye show seems to be hinting at him training Kate Bishop, a young archery prodigy and skilled combatant who eventually becomes the third Hawkeye in the comics.
Kate is introduced in the pages of Young Avengers, and many fans believe that the future of the MCU lies with their introduction of the team. Indeed, WandaVision is already teasing the idea of Wanda giving birth to Wiccan and Speed, and Avengers: Endgame ages up Cassie Lang to the perfect age for her to become Stature, meaning that seeing the Young Avengers on-screen might be much more than a pipe dream. If that were to be the case, having Hawkeye take on an ersatz leadership role for not just Kate, but the Young Avengers team as a whole would be the perfect way to bring his arc full-circle. If they wanted to take it a step forward, having Clint lay down his life to save the Young Avengers during a mission would be a fitting absolution of his shifting morality, making his sacrifice an immortalized example of the heroism Clint exuded in his best moments.
Hulk
The nature of The Hulk's licensing rights make it difficult to know just where Bruce Banner (Mark Ruffalo) will show up next, but there's a strong demand for Ruffalo's Hulk to show up in the She-Hulk Disney+ show. In the comics, Jennifer Walters is actually Bruce Banner's distant cousin, which is why she requires a blood transfusion from him after being fatally wounded by a gunshot. This, of course, is what turns her into the She-Hulk, so his presence in the show is almost required if the MCU wants to introduce her in a way that's comic accurate. However, beyond this, the Hulk's future in the MCU is really limitless as he's become such a versatile character in tone and personality.
Mark Ruffalo has expressed a desire to play the character for as long as possible, so he's another character who could very feasibly stay on Earth to train the rest of the Young Avengers, using his own mastery of his abilities as a sort of success story for younger heroes who are learning to control their powers. It would make total sense to see him help Jennifer Walters learn to curb her destructive tendencies as She-Hulk as well, and a perfect usage of the two characters could be a storyline in which they are searching for other people who have been exposed to gamma radiation in the same way that Bruce Banner was, bringing them to blows with potential returning Marvel characters from The Incredible Hulk.
Thor
Thor (Chris Hemsworth) is arguably the biggest name on this list, and as of right now he's the only one with a film coming out soon as well. For the most part, the MCU gave him a very defined arc throughout the first three phases, starting out as an impulsive and brash wannabe ruler who eventually learns that the most important thing to him is the preservation of life and the protection of those closest to him. Avengers: Endgame throws an unexpected curveball in his arc, however, when he decides to relinquish control of Asgard to Valkyrie, preferring the life of an adventurer and potential space-farer with the Guardians of the Galaxy.
With Thor: Love and Thunder re-introducing Jane Foster and giving her the title of Mighty Thor, it's safe to say that she'll be inheriting Mjolnir, leaving Thor without a hammer and without a kingdom to rule. It seems that for the most part Thor is abandoning his ties to Earth and venturing out further into the universe, which is a perfect vague send-off for a character that won't age like normal and can't be killed like a regular human being. Seeing Thor join the Guardians and potentially even take over a new iteration of the team would fit with his more nomadic status in the MCU right now, and turning Thor into an intergalactic legend dropping in to help planets and civilizations in need would be a clever way to retire Thor while keeping the potential for him to return in the future, because with the new threats being introduced into the MCU during Phase 4, our new heroes might need all the help they can get.