Yep, any torrent streaming application will do. Popcorntime works on android, but it comes with a pirate movie catalog built in. I might make a bounty for a fork of it that just plays links and has no catalog, I don't know yet. What would be best is of course a utility tthat opens the stream in your media player of choice, popcorntime has a built in media player, but it would work. I don't know if you've ever used Scrambled Exif, it's an application that strips exif data from images before sharing them, no UI, just share to it and then it opens the share dialog again, something that worked like that that just had a dialog open up asking which media player to stream to. I'm not an android developer.

For desktop there's peerflix, there's also a popcorntime client that doesn't have the catalog anymore as that's fetched remotely but it can still stream magnet links just fine.

What happens to the video... Same thing that happens if a host doesn't want to host anymore. Ultimately hosting costs money. "Free" hosts make their money in other ways. They censor, they delete old content. I would think a person who has a personal interest in their content being available would be more adamant about ensuring that, especially since all it takes is a seedbox. You can rent seedboxes if you want to pay for hosting. The goal isn't to ensure perpetual availability, as that is impossible. The goal is to make it easy for content creators to host and share videos without complex setups, and with nostr that includes a route to monetization which is spectacular, it's a big problem with every other approach to self hosting video content.