If someone has developed RSI because of bad technique, then can he/she play anymore? I believe I may have developed RSI and does not know anyone who has it that still plays.
RSI goes away after a couple/few days rest. I've had it before from practicing the same thing for too many hours and I just needed to rest it for a couple days
It may go away after rest, but it might have been caused by bad habits in the first place.

Check out this article I wrote on the subject:

Hand Mechanics

On my site I also discuss proper technique and avoiding these problems.

Have you been practicing especially hard recently?
Yeah I have... also! I'm pretty sure the strain from trying to unanchoring sorta got to me along with a decent amount of practicing with strain. I hope it goes away...