The permanence of an NFT may depend on the existence and stability of the blockchain network it relies on. If NFT is built on a stable, secure and permanent blockchain network, it will last longer.
I think blockchain in general are permanent, but it couldn't save the NFT file inside the blockchain it only records metadata, in saving NFT file one need other services, but actually, I don't think many really care about this, i too don't really care about how nft saved, just invest.