Can I trust you with a secret? A big one I mean, possibly a life changer, not just a locker combination. I'll chance it.
We're not doomed.
It always seems like it. The stocks of non-perishable foods have been picked clean, we don't have any major munitions factories running, the city states are gearing up for war, the aliens are copying earth vehicles, the pipelines have all corroded, no one makes the tools to fix the machines to rebuild the infrastructure to make the tools to fix the machines to re-
You know. Its been pounded into your skull with some regularity. None of this is false, but its not quite true either.
Fact is, you have already survived one of the most tumultuous uprisings and cullings since the black death, small pox, the second world war, or that volcano that reduced the human population to less than 10,000 a couple of millennial ago. If you can make it on Broadway, or through reanimates - you can make it anywhere.
Another thing for you - the chain of transmission for a lot of diseases has been broken. Hiding from the reanimates has been a quarantine enforced by an unexpected source. Nano-vac may be hard to come by these days, but the need for it has been dramatically lessened. Germs tend to go extinct when their carriers disappear.
It might take centuries to fully reverse the impact of the industrial revolution, but the air in many places is already cleaner, and the world on a whole isn't that unpleasant right now. We don't have the old over-crowding of the past few decades. Trade might be down, but we don't need it as much.
If ninety percent of humanity died, that means ten percent still lived, and ten percent of nine billion is still a big number. Enough to keep nations, religions, currencies, and art forms alive - we're not going to have one big happy family unified earth at the end of this, but humanity is going to keep chugging along for a while. Heck, so will you. Even without new sources of nano-vac, seventy or eighty is still easy, you just can't rely on tiny robots to do much of it for you.
Humans are still as adaptable as ever. We've made it over the hump. There are still challenges ahead, but extinction can wait for another day.