I'm not a veteran or a first responder or anything like that, nor do I have PTSD, but I did get into a similar problem of believing it was the end of the world (and before that, intense phobia of diseases), and getting carried away with it to the point where I lost the plot of my actual life. I got so consumed with this stuff that I didn't do what I was supposed to be doing, and I am still recovering from it and trying to catch up, even though it was years ago now.
I wish that instead of panicking and letting my emotions get the better of me, that I had instead calmly, rationally looked around, saw that other people were not worried, taken a moment to remind myself that I'm not an expert or the smartest person in the room and therefore don't have all the answers and that just because I haven't seen an answer doesn't mean that no one else has or that there isn't one, and just done what everyone else was doing/what I was supposed to do, instead of letting fear hijack my life.
I wish I had thought, giving up on life because of what I was afraid of would have been like someone in the generations before mine giving up on life out of fear of nuclear war, saying building a life is pointless, we're just going to get nuked any time now, maybe today tomorrow next year but it's going to happen, might as well quit. But that never happened, and we're still here, and a lot of the people that ignored the news and carried on like nothing was wrong all throughout the Cold War and just lived their lives, turned out just fine, and had a lot of good times.
I really regret all the time I wasted on this phobia and end-of-the-world crap, when my life could still have been very happy for a while yet. It pains me to this day.
While I don't have advice to give on your situation, I can empathize with this all-consuming fear of the end of the world and being convinced that it's going to happen, and what a terrible waste it all turns out to be, to spend your life worrying about it. I hope for all of your sakes that your husband snaps out of it, and you can both get back to enjoying your lives again.