Way outside my wheelhouse so take the following with a grain of salt, but TMK the company that “owns” Mastodon is a non-profit LLC named Mastoton gGmbH and probably isn’t technically worth anything by itself. Not that they would ever sell to you, but by purchasing, you wouldn’t own the codebase or any of the instances. The community would immediately fork the codebase, most of the members of the Mastodon gGmbH would leave and reincorporate as a new entity and continue their work on the codebase, and life would go on without much of a hitch.

Edit: Here is the official post that Mastodon made about registering as a gGmbH, which includes some important info about how a gGmbH works, and how it includes some some restrictions that really prevent any value from being extracted out of a potential purchase.