Once the twitter sale is completed, the new owner of twitter can chose whatever they want to do with it, including shutting it down - which in this milleu would be something that the buyer of twitter will consider doing just for LOL's.
imagine the trolling potential of a rolling outage of twitter or ooops "new owner" deleted the database as a joke. Or replace all twitter profiles with sayings from Doge.
before you say "this person can't possibly do this" ... think again.
That might be slightly over exaggerated. Musk may have other equity investors and certainly has other debt investors (assuming they come through, but then the whole deal hinges on it). So he still has some level of fiduciary responsibility. And a need to cover his Tesla stock backed loans with generated cash flow. Though how much impact that would have is definitely debatable, it probably isn't zero.
the individual owners/operators of each mastodon instance.
there is the mastodon project, but you can fork the code and make your own community if you want more control over your own codebase when it comes to your own mastodon instance
