DH & I have been invited to best friend's wedding overseas. We can't afford/didn't want to take our DC so before accepting we spoke to both sets of parents to see if they could babysit DC for the 2 days & 1 night we'd be away. My parents said they had the theatre booked on the saturday night but if we were stuck could try & rearrange or cancel (they go at least once a month if not more & finance wouldn't be the issue) but DH's parents were happy to come & stay so we accepted the invite & booked our flights.
It's now 4 weeks until wedding & MIL called earlier to say she's been put on a waiting list for a minor op that if it went ahead before the wedding (quite possible) would prevent her coming as she can't drive for 6 weeks afterwards & there's no way they can get here any other way. So, I called my parents to explain but they're now saying they can't baby-sit as they're going out. I asked if they could reschedule but they said no. End of conversation. So, we might not be able to go to the wedding & if we do cancel, it could be very short notice so no chance of refunds not to mention very unhappy bride 
So AIBU to be totally fucked off that my parents won't cancel some crappy theatre 'do' & help us out?