Lots of people are saying “you’ll come back” and “nobody is migrating for real”, and I have had the same opinion back when the Twitter deal was first announced and a few people moved over to Mastodon.
But this time, it was very different: When the deal went through, a large part of my bubble really did move to Mastodon. This happened over a few days, and after the second or third day, my Twitter timeline was noticeably empty, and Mastodon is very alive instead.
Of course I can’t predict if this sticks over the medium or long term, but for me, the situation is very clear: the people I care about are now on Mastodon.
(I spent 10 years on Twitter, with over 4000 followers.)