Responses
Extra:
That someone that changed the past must be connected to the enemy he and the "devil" encountered. Said enemy referred to the both of them as possible interferences with "the new world", as in, maybe, "the timeline that the one controlling that thing created by removing Sid from history"
WOW
*Salutes
The war ended 100 years ago in his normal timeline. Yet his friends are alive and of the same age as before. And I doubt they're 100+ years old. So he's not in the past. He's in an alternate timeline. So it's far more likely that someone changed the past to erase Sid from it and created an alternate "current time" where the four races weren't sealed.
What's interesting is this "code holder" thing. It might be something that Sid also possessed to become the hero of humanity. And now he has the sword as well. So my theory is that he will indeed be taking on the role of Sid, but only to fix the timeline and return it to how it once was.
Unless he later on travels back in time to actually become Sid of course, but there's nothing indicating that so far.