You're 100% wrong on the details.

A few things:

1. Lemmy runs on an open protocol which cannot be "bought", known as ActivityPub. All platforms that use ActivityPub can theoretically interact and federate with Lemmy. This means that if something like lemmy.world was bought, we don't have to "move away from it", we just spin up another instance and then federate with it while the other instance doesn't have to deal with corporate things like ads.
2. Lemmy is Free and Open Source Software licensed under a version of the GPL. This means that it can never be fully restricted, and if corporate interests were to theoretically "buy" the current maintainers, it can be forked to a version without corporate meddling, which can then federate and interact with all the current instances anyway, due to how ActivityPub works.
3. There's a lot of instances. You can't buy the entire fediverse as you will have people with principles.

Now don't get me wrong, they can absolutely meddle, but not purely through money or hostile takeovers, due to the decentralised nature of the Fediverse. No matter what, the Fediverse will always exist as it is, all the huge platforms can do is try to make it so people don't want to use the Fediverse and move to their platforms instead.

To try and give an analogy, it would be like a company trying to "buy the web" - they literally cannot. Of course, we do have some huge players who control a lot of the web and attempt to dictate standards for everyone else, but there is no one iron fist that rules over everything, and there's many small players and communities all over the place.