In a direct strike, they'd be ionized and finely distributed. Maybe a little weight loss due to transmutation and decay, but I'll likely not be keeping close track.
The obvious answer would be to dig a super strong bomb shelter just big enough for your coins, and bring a PCGS inspector to grade your shelter at least ms67.
Well, in the case of a nuclear war, I doubt I will be worried about my coins. "If they let it all fly", I doubt anyone will really have time to worry about anything.
If my family and I are vaporized, or dying of radiation poisoning, I really won't care what happened/happens to my coins.
Speak for yourselves. I'd be safe and sound, along with my valuables, in my EMP resistant nuclear powered spaceship jetting off to one of my many out of system vacation stations. I mean, since we are talking hypothetical nonsense here. Guy