I think you misunderstand how the expansion of the universe works. While the universe is expanding, it does not do so at a uniform rate on a local scale, as that expansion can be countered by various forces, most notably gravity. It’s expected that while space will continue to expand, stars within galaxies and groups/clusters of galaxies will all remain bound to each other for as long as that gravitational effect persists. Within the Local group (of which the Milky Way is part), for example, there are at least 80 galaxies, and those will stay bound indefinitely (according to our current limited understanding). Galaxies outside of our supercluster are, however, already moving away from us faster than the speed of light, so exploration outside of a supercluster without FTL tech would be impossible.

As for the accessible resource issue, that’s a fair point, and one I hadn’t considered. I imagine we would be able to repurpose already collected and refined materials from our old civilizations as a way to somewhat offset that, but it would definitely be a major hurtle to get past, especially if radioactive dust is a hazard we need to deal with on an atmospheric level. I still think humanity would find a way, as our ingenuity shouldn’t be underestimated, but I don’t think it’s a guaranteed thing at all, and I acknowledge my only reason for believing that is just a gut feeling and a, frankly, selfish desire to believe we aren’t as vulnerable as we appear to be.

Nonetheless, a humanity that barely clings on isn’t much of a win in either case, so even that is a cold comfort.