Zim,
If nobody has the key, I expect the crypto has then seen its last transaction. It exists in the blockchain but nobody can use it, without the key.
On the other hand, if anyone has the key, then the servers getting destroyed is not a problem...
I imagine, but don't know for sure, that when you 'put' your crypto in an exchange, they get a key and your key no longer works. (They become the de facto owner, and you have a security interest only).
So, if they don't have a backup of their key, the crypto is "lost" to all parties. But, hopefully, you can sue them for negligence and get your value back.
I'm not a crypto expert, but if I had crypto I'm not sure I would store my crypto in an exchange. And I don't think I would carry it around in a "wallet", either (well, maybe a little). It is fairly common these days for someone to steal a phone, and either break in to it, or FORCE you to open it, and then transfer out all the crypto.
I think 'losing' your crypto is really quite easy to do. And when you lose it, you likely don't want to be too public about your loss, either. Because bad characters will otherwise know who to visit?
That is one thing I don't like about crypto.
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