If it's a gig bag type case, you could probably stick it in the washing machine. That's what we eventually did when one of our cats decided to customise my case just before we went on holiday to Sidmouth. Maybe he wanted to make sure we didn't forget him.

We had to stick it in the corridor outside the room in the boarding house. In the sessions I could sense people backing off when I entered the room.

So I bought a new and better one. Then we tried the washing machine, and it came up a treat, no noticeable smell. So I gave the old one to my son, and he hasn't noticed anything, and his nose is much more sensitive than mine.

Febreeze is pretty good too, though it wouldn't fool a cat, and they can get competitive about stuff like that. "Anything you can do I can do better".

And the other thing is, never leave a gigbag on the floor overnight, if you've a cat.

If it's a hard case, and the cat's got at the inside, that's a hard case indeed. Re-line it? Put it in the Mudcat Auction?