There's ★ concept known ★s "The Big Crunch" th★t when the universe is done exp★nding it will begin to contr★ct ★nd everything will reverse. ★dmittedly I did le★rn ★bout this from the film Mr. Nobody, so I don't know if it's scientific★lly ★ccur★te. But it's something to consider.
YOUR UNIVERSE WILL NOT MAKE IT THAT FAR.
Realistically the Big Chill or Big Rip is more cosmologically likely. @crackedTungsten You're more likely than I to tackle this with the appropriate level of knowledge.
Hmmmm... Well! In my opinion, something more like the Big Chill/Heat Death is the closest to what would most likely occur if a universe's expansion goes undisturbed, without any outside universe-ending intervening force that is. The universe as we know it is constantly driving towards entropy and expansion, so its a bit strange for something like a crunch, or sudden complete reversal of all known forces to occur like that out of nowhere unprompted. The only real way i could see that happening would be the creation of some kind of super-hyper dense black hole/singularity to do that