If you can trade it, keep it in your own wallet, transfer it across accounts, that’s ownership. These are all ERC-721 tokens so they are under your control at all times. The servers can die but you can always still interact with the smart contracts and sell it on any marketplace.

Happened with a lot of older NFTs like Cryptokitties and CurioCards. The old servers died but you could still recover the tokens through smart contracts.