Unless Twitter completely turns things around (spoiler, they won’t) I expect Threads will slowly grow over the next several months; both in users and features.

At the moment Threads isn’t ready (from a functionality standpoint) to absorb Twitter, but it will be the more time they have.

From a Mastodon/Fediverse standpoint the sooner Twitter falls over, the better. (Assuming it’s ready to scale and take on users, I think probably, but who knows.)

In short unless something dramatic happens I expect Threads (for better or worse) will be around for a long time.