It would suck to lose JCL. I'm not positive whether he's still our starter at the end of the season, but at the very least he would be starting at the beginning of the season and a key depth piece, one of the first off the bench.
That said, I think Underwood's personality as a coach is about as different as you could imagine from Groce's, and it's not going to mesh with everyone. Indeed, I was just listening to a podcast with Bob Huggins the other day, someone asked if he or Martin was the "bad cop" at K-State, and he said "if you think we're tough, you should see Brad Underwood". We need some of that toughness -- Groce never seemed to get the best out of his players after his first year -- but Underwood's style might not suit everyone. I'm not shocked that this is a possibility. Hopefully JCL stays but if not, good luck to him.