Rip Hunter died in the Legends of Tomorrow season 3 finale, but his story might not be over. As a a part of the climatic battle with Mallus, Rip sacrificed himself to give his former team time to save themselves. The death of Rip had been teased before on Legends of Tomorrow. Season 2 opened with Rip mysteriously disappearing and a large portion of the Waverider crew assuming he was dead.
However, the death that Rip suffered in season 3 finale, "The Good, The Bad and The Cuddly" seemed rather permanent. It closed out a character that Legends of Tomorrow had appeared to outgrow. Rip originally brought the Legends together but had almost disappeared in season 3. (Although some of that was due to actor Arthur Darvill's availability.) Despite appearances, plans are already forming to bring Rip back. He won't be the only previously departed Legend to return either.
Nothing is definite with Rip's return. However, in an interview with Entertainment Weekly Legends of Tomorrow EP, Marc Guggenheim, explained that the show wants to have Rip and Darvill back for season 4. The producer explained:
We love Arthur, we love having Arthur on the show, and I think Arthur enjoys being on the show. Because it’s a time travel show, and because we never saw a body, anything is possible. I think Arthur is totally willing to come back and play with us if we have a cool idea.
It would feel a little cheap to undo Rip's death. Even there was no body, Rip's death gave the fight against Mallus some necessary stakes. Resurrecting him would retroactively undo the impact of the battle. However, Legends of Tomorrow has already used time travel effectively to have the Legends crew interact with deceased characters, the most notable example being Captain Cold.
While Rip returning in some fashion is up in the air, the other big return is definite. The season 3 finale had the team lose a huge member. The episode closed out Amaya Jiwe's story. Amaya's story ended, not by death, but by having her complete her destiny and go back to her original timeline. However, actress Maisie Richardson-Sellers is still signed on as a series regular for season 4. Guggenheim isn't tipping Legends of Tomorrow's hat just yet. Vixen will, however, be back. Guggenheim elaborated:
Maisie will absolutely be back. We just felt like we owed it to the character to complete this arc, complete this story loop that we got her in. Once we took her off of her path in 1942, it was always incumbent upon us to return her to that path. That was something that hung over us as writers, and hung over the character… I’m looking forward to a different storyline for Amaya next year. We’ll reveal our plans for Maisie’s character at Comic-Con this year.
Given Legends of Tomorrow's penchant for insanity - a telepathic gorilla attacking a young Barack Obama was an episode's C-Plot - the method of Amaya's return could be anything. However, some clues could be read into Guggenheim's confirmation of Richardson-Sellers' contract continuation. This is pure speculation but it's, obviously, not out of the realm possibility.
It's interesting that Guggenheim acknowledges that Amaya's story ended with the season 3 finale. Yet, he also makes it clear that Maisie will be back, not necessarily the Amaya that was left in Zambezi. Although it's given an Amaya will be involved. It just might not be "our" Amaya. Given the fact that Legends of Tomorrow is apart of a multiverse, the show could close the door on one Vixen and introduce another. Perhaps the way that Legends of Tomorrow will get around giving Amaya such a perfect end and keeping Richardson-Sellers is to introduce a new Amaya from another Earth. This would allow Legends to keep Amaya's story complete and do whatever they want with a brand-new version of the character.
The Arrowverse has already done a similar thing with actress Katie Cassidy. Katie Cassidy's character, Laurel Lance, was killed in Arrow season 4. Yet Cassidy was brought back as the evil Earth-2 version of Laurel, Black Siren during The Flash season 2. Black Siren and Cassidy later rejoined Arrow as a series regular in season 6. Legends of Tomorrow probably won't copy Arrow exactly. An evil doppelganger Amaya would be interesting but maybe unsustainable. However, the precedent of alternate Earth versions giving new life to finished characters has already been set. After all, the multiverse is one weird section of the Arrowverse that Legends of Tomorrow, somehow, hasn't managed to touch upon, yet.