Unless you or anyone else has a copy of the file, then they can put it back and the URL will be the same. If you own an NFT that points to something on IPFS you

Unless you or anyone else has a copy of the file, then they can put it back and the URL will be the same. If you own an NFT that points to something on IPFS you probably want to keep a copy of the file lying around to do this if necessary. There are projects trying to create permanent decentralised, content addressable storage (in some case as layers on top of IPFS), so maybe even that problem will go away.