My band has been offered a slot at a local art fair. We can either take the Friday night headliner slot, but we would need a sub for our guitarist — or — we can take the Sunday afternoon slot with our normal lineup. Everybody agrees the Friday slot is more desirable (high-profile, late nite party vibe, & cooler weather). The guitarist is not jumping at the chance to take one for the team and sit out since we have the Sunday option.
FWIW, I’m not crazy about acting like any one of us is expendable for the sake of a gig. Then again, maybe the guitarist is putting himself above the interests of the band? We have plenty of shows on the calendar, and our primary motivation is to play fun gigs for good crowds. Money is not an issue for us.
What’s more important to you …the gig or the band?
I'd do Sunday with the normal lineup. Your guitarist is on vacation and it sounds like that was clearly blacked out for him in advance. You get offered a gig with an option for either his blackout date or a few days later when he's back. I don't think he's "not taking one for the team" because he's available for essentially the same gig (I don't mean the night or crowd) a few days later. It'd be different if there was no option for Sunday, then by all means use the sub. Seems to me, you'd just be rocking the boat by taking the Friday gig.