Ok I was mistaken. That’s a different problem entirely then. If they were elevated by a licitly consecrated bishop then they’ll stay bishops.
Ironically, SSPX is a much more serious breach than any of the Protestants, we never lost a bishop there.
Oh, I’m sorry to say we lost at least a few bishops to the Protestants. Mostly in Germany, Scandinavia and England. When you think about it we’re actually gaining bishops with SSPX! And soon that will happen (sort of) with the Anglicans too. Interesting times!