There was a Simpsons episode where the evil character had stolen a nuclear weapon. At the moment of detonation they did that freeze frame on several of the characters, just as one of the famous apocalyptic movies had so successfully done. Then they focused in on the blast and it fizzled. Lisa bends over and reads the tag which says, “Best by November 1959.”
I do understand there are some deteriorating elements, which was why nuclear testing was so important. But I’d wager we’d get some hideously dirty explosions even if they don’t work correctly. Let’s say it’s only .5 megatons instead of 5. Still pretty messy.
Granted, I wouldn’t go pushing buttons on a nuke even if it was stamped “1429” and I pulled up out of an old creekbed (maybe especially then, LOL). There are some things you just don’t mess with. Nevertheless, reliability decay is a big issue with these things.