Good question. With Mastodon, there is no central data store. So if your chosen front-end goes down (which hosts your content), you're out of luck. I think they're working on that problem though.
It's weird to me how the no-retractions thing is a benefit. Seems like a feature deficit. I can't imagine using twitter without the delete function, if only just to delete botched tweets.
I can think of lots of situations where that's not a good thing. I can't really think of any situations where it's a good thing.