I just had an idea in a sci-fi setting for an alien race that has re-emerged, but I don't know how plausible it is or if there is anything to make it more plausible.
Consider a conventional universe, just with an FTL method of travel, on another plane of existence as not to overlap with reality.
The alien race years ago went underground as their sun was dying and managed to survive in the subterranean setting. Their sun died, and all was good. Fast-forward now to their re-emergence. They came out of their subterranean realm because life had returned to the surface thanks to their/a sun now being there.
So how does this happen, and how likely is this to happen?
I have a few ideas:
Their solar system drifted through something that added enough matter to their sun and displaced enough of what was there to give it enough fuel to reignite. Mental simplification: a snooker ball smashes into another and effectively replaces it.
Their planet, once the sun had died, drifted out of orbit and through dead space for a time as a rogue planet before being captured and settling into orbit around another sun.
The Wizards did it. I don't like this option as it's just lampshading it, and also potentially introducing a power capable of stellar engineering. That concept alone outweighs the reappearance of this ancient race unless it was the ancient race, and I don't want them to be at that advanced level of technology.