This is what happened with GitHub after the MS acquisition announcement as well. Right after the announcement there was a HN post about repo creation/imports being up 1000% or something, but now we can tell that not too much has changed (and GitLab was free hosted as well; you have to run your own mastodon instance). Until mastodon itself brings some killer feature that makes it de-facto better than Twitter, or Twitter actively starts promoting hate speech to people who otherwise are only interested in the art / 'art' parts of the platform, then it'll still be relevant even if it's bleeding a lot more money than it used to.