Star Wars comics have guaranteed the return of the Jedi and the Sith inevitable. The history of the Star Wars galaxy is essentially one of constant conflict between adherents of the light and dark sides of the Force. Even galactic politics have always been dictated by the Jedi and the Sith; the Galactic Republic was founded after the defeat of Darth Bane, and Palpatine swiftly established a new Sith Empire when he rose to power a thousand years later.
It's entirely possible the Chosen One was born to bring an end to this conflict. Anakin Skywalker participated in the slaughter of the Jedi, after all, before going on to bring an end to the Baneite Sith. Viewed from that perspective, it's surely no coincidence Rey - surely destined to found a new Jedi Order - appears to have learned from ancient texts that predate the schism that created the Sith. She hopefully has the potential to build something new, a Jedi Order of true balance. But recent Star Wars comics have made the return of ancient Sith and Jedi seem far more likely.
The timing is no coincidence, of course, especially for the Jedi; Lucasfilm's Star Wars: The High Republic transmedia initiative has proved there is massive interest in the history of the Jedi. Writers are understandably tempted to draw together the narrative threads of different eras, and readers are eager for just that kind of transmedia experience. But the sheer scale, and the potential return of Jedi and Sith, are surprising all the same.
Star Wars' New Force Vergences Give The Galaxy A "Memory"
Star Wars has introduced several planets rich in the Force, so-called "Force vergences" that possess unique properties. The most well-known of these is Exegol, introduced in Star Wars: The Rise of Skywalker, a planet where the veil between life and death is unusually thin - explaining why Palpatine could be resurrected there, and why the voices of dead Jedi could speak words of encouragement to Rey. But Charles Soule and Marco Castiello's Star Wars #20 introduced a vergence that could be even more important, the Living Sea of Gazian. This world takes an imprint from any Force-user who visits it, and anyone who plunges into the Living Sea of Gazian can commune with these imprints. The Living Sea of Gazian effectively gives the galaxy a "memory," one that can be accessed with ease. No secrets of the Jedi or Sith need ever be lost, for it is always possible to learn from Jedi and Sith of the past.
The Jedi always guarded the locations of Force vergences, explaining why the Living Sea of Gazian is little-known. But it was certainly known to Jedi of the High Republic Era, and it was discovered by Luke Skywalker shortly before the events of The Empire Strikes Back. The interesting question is whether the Sith ever knew of its location; a Holocron message from Master Yoda reveals several vergences served the same purposes, and it's notable the other two he named were destroyed by the Empire (the Jedi Temple on Coruscant and Jedha's sacred temple, respectively). Presumably Palpatine targeted these vergences because he sought to destroy all record of the Jedi, including those provided by the Force. The Living Sea of Gazian would have been too vast to destroy by anything other than the Death Star, though; if Palpatine did know of its existence, then Luke Skywalker likely saved it when he blew the battle-station up.
The Living Sea of Gazian provided Luke with visions of the past and future, clearly possessing powers that transcended the nature of time. But it was undeniably influenced more by the light side of the Force, a vergence of the light that had been influenced by countless generations of Jedi. It's fascinating to speculate whether similar vergences had been discovered by the Sith, and twisted to their own purposes, thus becoming aligned with the dark side and leaving a permanent record of their evil order.
The Fermata Cage Would Allow An Ancient Sith To Return
Recent comics have revealed an even more direct way for ancient Jedi and Sith to return - exploring a new method of time travel in Star Wars. It seems the ancient Sith heretic Darth Momin discovered a way to use the dark side to manipulate time itself, constructing a device he called the Fermata Cage. He used ths to place a Sith Lord outside time, trapping them for millennia - until the events of Charles Soule and Steven Cummings' current Hidden Empire miniseries. Set before the events of The Empire Strikes Back, this story tells of a desperate battle between the Empire and the criminal organization known as Crimson Dawn. Lady Qi'ra, the leader of Crimson Dawn, has dedicated herself to overthrowing the Sith - and she believes the best way to do so is by restoring another Sith to the galaxy. The dark side is competitive and adversarial, and she rightly believes another Sith woud attempt to overthrow Palpatine and Darth Vader, resulting in chaos on a galactic scale.
Qi'ra seems to be right, because Palpatine is surprisingly scared of the Sith's return. He has created a civilization steeped in the dark side of the Force, which he channels and manipulates, but any Sith who returned in that period would inevitably benefit from it as well. The Hidden Empire event is clearly building up to the opening of the Fermata Cage, and it's impossible to say for sure what will happen when the Sith within emerges. Meanwhile, what has been done once can be done again; there's no reason to assume the Fermata Cage is the only device that locked a Sith or Jedi outside time.
The Spark Eternal Is Another Terrifying Threat From The Past
Finally, the ongoing Doctor Aphra series (written by Alyssa Wong and illustrated by Minkyu Jung) has unveiled a new technology that preserves the minds of people from the ancient past. The Spark Eternal was created by a Force cult known as the Ascendant, and it has the power to transform anyone into the equivalent of a Sith. The Spark Eternal has been absorbed by Doctor Aphra, and it is clearly attempting to set up a confrontation with Darth Vader himself. But these stakes may be even higher than the potential return of the Sith; there have been hints the Spark Eternal will threaten the Force itself, presumably an alliance of technology with the purpose of wiping out all life across the galaxy. This, ironically, could be an enemy that forces Star Wars' Jedi and Sith to work together.