I don't think it's out of the realm of possibility that this could be the end of the US.
I would say that it's fairly likely that it is the end of the US as we know it. With stuff like Project 2025 combined with Trump's talk of going after his enemies, it's fair to speculate that we're going down a dark road that could end up being like Russia (where elections are not real, where actual opposition politicians or even people speaking in opposition get taken out. MMW, the right would still claim that they're free speech while taking out people for speaking out. This is exactly the kind of Orwellian nonsense I'm used to from them) and could end up being a theocracy which would knock us way down in so many metrics.
As for if the empire collapses, there is civil war, etc. I don't know about that. If the people voted for this monster, I can't see the latter happening. I mean, what are the state governments going to fight over? Will a blue state really fight with the federal government over cutting funding because they legalize abortion? TBH, I see the blue states throwing our rights under the bus before causing any such tension. Both scenarios are scary and not at all out of the realm of possibility...
I live in Colorado, so idk we will see if the Federal Government wants to go to battle with us. But Idk we were the first state to legalize marijuana for medicinal and recreational, so idk we could be a first to just give the feds the ole finger if they try to restrict abortion rights here or do any of their gross 2025 project, point being yes I think blue states could fight back perhaps.