Threads will mainstream threads.
Any good content here will be available to the Threads users, who will be oblivious to where it is coming from.
Eventually, Meta will take steps to break compatability, and lots of the most prolific contributors from here will move to Threads exclusively (for a host of valid reasons).
When it is no longer in Meta interest to federate, they will stop.
The fediverse will continue, but it will be weakened by it’s temporary reliance on Threads (who could afford to host large images/videos/etc, have lower latency, etc etc).