Yes the line up is good, yes he's a great drummer, but by the same token, he's only a drummer. He doesn't write songs, he's not the most visible guy on stage. He's a good personality yes, but when it comes to the music, as much as it pains me to admit it, I think Nicko is the most replaceable.
Depends on what God tells him to do. Neal Morse quit Spock's Beard after much prayer and meditation, so it could happen to any of these crackpot born-again Christians.