I don't think I've ever required my kids to stay in something they wanted to
quit. I have discussed it with them - Did it not turn out to be what they
wanted or expected? (which, I think, has been the case most of the time),
Did things change on them? (a musical dd was involved in added a bunch of
Saturday rehearsals at the last minute (along with the Wednesday
rehearsals), and we were already busy those Saturdays. That time, we talked
about it with the director and dd just missed a few (she was only a chorus
member)), How would they feel if they left?, or How would they feel if they
stayed? But I emphasize to them that the choice is all theirs.

My kids are pretty persistent in things they care about so that's not a
concern of mine.