It depends on the instance. Larger instances do have backups, and they have operational funding. There is also a history of these instances operating for years

It depends on the instance. Larger instances do have backups, and they have operational funding. There is also a history of these instances operating for years without issues. Mastodon also makes it very easy to extract your data. Finally, you can always run your own instance if you wanted to and have full control over it.