Google the history of xmpp. This is exactly the same.
It’s not a good thing.
So we can let Mastodon die on the vine or chance it dying? Ok, I know my choice.
It’s not like the majority of people are already on open protocols. I’m sure Threads dwarfs Masrodon usage just as Twitter and possibly even BlueSky.
IF Mastodon was dominate I might have a different view but it’s not. If Threads federates then there is an opportunity to push people to other clients which make switching to a Mastodon/ActivityPub server much easier. That’s literally only upside. It’s not like the people on Mastodon now are going to leave it for Threads.
They might end up being forced to, should Threads decide to revert.
Mastodon users will inevitably hook up on Threads communities instead of fostering their own, and at that point being left to their own devices would be a catastrophe.
And yes, this is exactly what happened to xmpp.