But, this is a very possible means private key will be lost.
As long as he saves the signed transaction, it's not a huge deal if the private key is lost. He just has to wait until we get back to 1 sat/vbyte levels (or whatever his transaction is paying), and then rebroadcast the transaction then. His coins are stuck in limbo for the time being, but as long as he doesn't lose the signed transaction, his coins aren't lost. Alternatively, once nodes will start accepting his transaction in to their mempools, he can make a CPFP transaction to confirm the coins.
OP, what software did you use to sweep the private key? There's a small chance it may be saved somewhere and you could try again. Although why you would ever destroy a private key is beyond be:
Sigh... why delete a wallet instead of moving it aside and keeping the old copy just in case? You should never delete a wallet.