I guess at least if you keep a copy of your NFT you can start serving it over IPFS yourself if whoever is hosting it can't be bothered anymore, or pay a service to on your behalf. It's sort of the ideal use-case for content-based addressing, I would think, since you're trying to prove some sort of connection with/ownership of/patronage over a piece of content. And it should be more long term resilient than a centralized solution as long as the NFT owners themselves don't lose their own files. At least the incentives are aligned (if you own the NFT you will want to keep at least one copy, if only so you can show it to potential buyers!)

It seems a substantially less silly idea than pointing a token at a url that you don't control. I guess I'm surprised that NFTs aren't all hosted on IPFS or something like it, if only as a backup. Like, have these people not heard of linkrot?

But I guess as long as the buyers don't realize yet that their immutable ledger entry can become a dangling pointer in a puff of smoke, it doesn't matter.

Yes, not dissimilar from torrents. Instead of being name-addressed and requiring the name owner to provide the infrastructure to serve the data (as with HTTPS), data are content-addressed so that anyone can serve the data.

Many NFTs are hosted by NFT platforms, and also by services such as https://nft.storage/ (backed by IPFS & Filecoin). It's quite trivial though to take the IPFS CID and pin it somewhere else (local computer, a pinning service like Pinata, etc.), and anyone can do it at any time. If all you want to do is be able to prove ownership at some point in the future, you don't really need to host the content indefinitely on IPFS...just host it when you need to.

Filecoin that you pay to have any files you like mirrored by many people, in a decentralized way.

Arweave is also a one off fee to have the file mirrored forever, the hosters are paid from the yield earned on that fee.