I disagree that the lack of a hard answer to the Fermi Paradox necessarily indicates that any technologically advanced civilization must invariably end up destroying itself. There are a variety of potential explanations that could explain our apparent solitude, of which a technological great filter is but one. For example, our universe is quite young, both in terms of how long a universe lives before its heat death and in terms of how long a universe continues producing stars capable of sustaining life. With this in mind, it’s entirely possible that we are simply the first to achieve sentience in our galaxy (as intergalactic travel is an unlikely prospect), especially if there is some particularly difficult evolutionary hurdle that we have already passed. Alternatively, it may be that communication methods detectable by us (such as radio emissions) are methods used only by technologically primitive spacefaring species, and so it could be that there is only a short window of time during which a species is visible to observers outside the system. And those are just two of a myriad of potential solutions to the paradox.
Space is vast, and the fact that we haven’t found anyone else yet should not be taken as proof nobody is out there. That’s like scooping a cup of water out of the ocean and declaring there are no fish in the ocean on the basis of that cupful of water alone. Looking more toward earth, I also want to note that humanity is a tenacious bunch. We have survived ice ages and super volcano eruptions in our past, climate extremes that mimic what could be produced by nuclear war. Undoubtedly, many of the outlined scenarios would be unpleasant and lead to an unacceptable loss of both human and non human life, but I find it unlikely that humanity wouldn’t cling on. Even if 99.99% of humanity died, that still leaves 800,000 people alive, and I doubt it would take more than 1000 years before we were back on our feet.
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.