Despite Ubisoft being rocked by misconduct and toxic workplace allegations, which now include the Assassin's Creed Odyssey director, it's unlikely the AC franchise is going anywhere anytime soon. Hopefully, Ubisoft is genuinely dedicated to improving itself as a company and putting out content without so much strain on its workers for its fans. The next installment, Assassin's Creed Valhalla, likely bears these same scars, but future games might not.
Nonetheless, focusing on the game itself, Assassin's Creed Valhalla and Odyssey could very well do something that no other two games before it has done: the protagonist of Odyssey could very well be alive and play a role (although likely minor) in the next game.
Assassin's Creed Odyssey Secret Ending
There have been moments that leaned into the franchise's science fiction elements and crossed boundaries, such as when Ezio spoke to Desmond in a room with Altair's corpse. Arguably, this is trumped by the secret ending of Odyssey, where Alexios/Kassandra meet Layla face-to-face. Their duty was to pass on the staff to her, with it keeping them alive for an extended period of time. Alexios/Kassandra was 2400+ years old at this point, passing finally after the staff changes hands.
With this in mind, it's not impossible that Alexios or Kassandra play some type of cameo or minor role in the new game. At the time, Alexios/Kassandra are roughly 1200+ years old at this point, but as proven by the suit they wear in the secret ending, they were no strange to the world around them. They can't let go of the staff, but they can't die either.
Assassin's Creed Valhalla and Odyssey
It's worth mentioning that the potential for this unique moment is there, but that this doesn't necessitate it will happen. This is pure speculation, after all. However, if it does take place, it's worth asking in what way this could happen? Chances are, it may play out to be a minor cameo, with Eivor spotting Alexios or Kassandra somewhere, completely unaware of who they are. It could be a passing moment in a marketplace for all it's worth, and it would still be a defining moment.
The second most plausible scenario is that Alexios or Kassandra have spent time working with the Hidden Ones and serve as a minor role in AC Valhalla, perhaps as a guest-giver. It's possible that Eivor has to do specific tasks for the Hidden Ones prior to joining or just due to being allies, and Alexios/Kassandra could crop up in some way. This wouldn't really be hard to explain, either, as Eivor would have no idea just how old they would be.
Another possible scenario, but arguably the most unlikely, is Alexios or Kassandra playing a major role. Perhaps through Eivor and Eivor's interactions with these figures does Layla learn how to control the staff fully and not be corrupted by it. Of course, with the franchise seemingly building up to another big event, this game could serve as Layla's Assassin's Creed 3, with the Odyssey character's guidance through the eyes of Eivor.
Either way, with Alexios or Kassandra living for quite so long, the potential and possibility for their appearance in AC: Valhalla is there.
Assassin's Creed Valhalla releases November 17 for PC, PS4, PS5, Stadia, Xbox One, and Xbox Series X.