The InterPlanetary File System is a protocol and peer-to-peer network for storing and sharing data in a distributed file system. Being a p2p network, chances are low for IPFS to go offline. However, you can host your own IPFS node and save the files in this node. Make sure to pin the NFTs files. Pinning a file tells IPFS that the data is important and shouldn’t be removed when the node is near its disk space limit. By doing so, you can ensure the persistence of the NFTs.