John Parker, played by Carl Lumley (and I know this off the top of my head, having seen BB about 300 times). The real question is why John Parker was sitting in with the band earlier in the movie, before they'd even met. Yes. Go back and look.
Okay, you convinced me; it's time to do a full-on Buckaroo Banzai / Jack Chick mashup for the whole world, by which I mean probably just you and me, to enjoy. As soon as I actually see the movie...
I thought Buckaroo parachuted out of the little fighter-ship at the end and John Parker piloted it away, presumably back to the mothership. Where did John Parker die? I admit I wasn't watching very closely last night. Now I want to watch the club scene again and see if it is John Parker playing drums. They didn't offer a No-Prize winning explanation for that continuity error.