First, Mastodon isn’t the only option - it’s not like both couldn’t fail just as both AIM and MySpace did.

Second, Mastodon runs on open protocols. That has good and bad points - for example, it won’t grow as quickly as a project with huge corporate backing - but it does mean that there’s a more direct link between the community and its longevity. Twitter isn’t just flailing because Musk is doing management by bong rip but also because he’s desperately trying to get out of a financial hole. Open source projects have different kinds of financial challenges but they’re never on the hook trying to fill a hole measured in billions of dollars, either. Given the number of communities older than Twitter I’d say it’s far from proven that Twitter will outlast anything.

I found it really interesting that one of the main Iceland instances is being run on a Raspberry Pi out of some student's living room in Sweden. Over 500 users at the moment. https://types.pl/@tritlo/109383888427885539

why? a single app running on a single server is several orders of magnitude more resilient than a spaghetti clusterfuck of services upon services. twitter could be brought down by a single expired certificate