Re: Moral Dilemma: What would you do?
Two years ago I got asked to fill in for a gig because the drummer kept missing gigs for various reasons - the last being an injury sustained during a hunting trip. I played the gig with one abbreviated practice and less than one week with them under my belt, and more than half of the songs were originals that I obviously didn't know. The band was pretty impressed with my playing cold like that (I listened to some of their demo recordings to get some familiarity of the songs).
So the other drummer shows up at the gig, and after listening to us play, knew he was in trouble. He begged the bandleader to get his job back but they eventually said they were giving me the job. It was very awkward for me, since I was caught in the middle and didn't want to start off by pissing off someone. I thought I was just filling in for one gig, but two years later I'm still playing with them. I was fortunate in that the band decided whether they wanted him or me.
You seem to be going way over and above the call of duty here, by offering to switch instruments, thereby putting yourself at risk of being shuffled out of the band at some point. I would have told him that I gave up other gigs for this one, and see what his reaction was. He should understand, and if not, then he's being the jerk and then I wouldn't offer him anything.
"Through many dangers, toils and snares..." - Amazing Grace, third verse