After his escape in the season 6 finale of The 100, Sheidheda (a.k.a. the Dark Commander) is likely to come back as an antagonist in the final season. The season 6 finale, “The Blood of Sanctum”, doesn’t do a lot to clarify where Sheidheda went or where he might come back again, but there’s enough to get an idea of what role he might play moving forward: an antagonist in The 100 season 7.
Throughout season 6 of The 100, Sheidheda acts as a secondary antagonist, with the Primes being the main obstacle to the protagonists throughout the season. He starts as just a voice in Madi’s head, one among all the other Commanders that live on in the Flame — a computer chip worshipped as a holy object by the Grounders. He slowly corrupts Madi over the course of the season, eventually possessing her completely. Sheidheda allies with Russell Prime, but Madi takes control back just in time to prevent Clarke’s death and possibly get Sheidheda out of Madi’s mind.
It seems like Raven manages to save the day at the end of season 6 by destroying the Flame, but it was revealed that Sheidheda had outsmarted them. By connecting himself to the computers on their ship, the Eligius IV, Sheidheda transfers his consciousness into the computer and then uploads it to somewhere else. No one is able to figure out where he went, but with the battle against the Primes finally being resolved and Madi barely surviving the ordeal (followed shortly by Octavia’s disappearance in the Anomaly), no one on the show has yet put much effort into figuring out what exactly happened to Sheidheda.
The writers had the opportunity to kill Sheidheda off easily, as his arc of corrupting Madi using her grief over Clarke’s apparent death was clearly over. Had they killed him off, it would have been a satisfying ending, so they clearly have a need for him in season 7 of The 100. He has a role to play, possibly as a major antagonist given how irredeemable he was presented as. The most likely role for him to play from this point forward is as an AI on his own, outside of the Flame, controlling one of the spaceships. He was on a computer on Eligius IV, but there’s also the Eligius III ship out there, with unknown capabilities. Eligius IV carried missiles that ended the world for the third time, though it’s unclear if there are more weapons on it. Eligius III was intended for space colonization, rather than a mining mission like Eligius IV, so it’s unclear if it would have weapons on it either.
While those are scary possibilities, Sheidheda doesn’t need weapons to be terrifying. He could be in control of an unarmed ship and still cause chaos and destruction. He was called “the Dark Commander” for a reason: his power was in demanding and obtaining loyalty through terror. Before Madi managed to stop him, Sheidheda woke up everyone still in cryosleep on Eligius IV, a combination of Grounders with loyalty to the Commander and dangerous, expendable prisoners from the Eligius IV mission. This could be a terrifying army, and he may be in the perfect position to influence or coerce them into his service.
Whatever form he takes, Sheidheda is far from gone from The 100. Raven couldn’t stop him from escaping at the last second and no one knows exactly where he went. Rather than a respite from his terror, it looks like a big conflict in season 7 is going to be his return, possibly as a more prominent antagonist.