Guests cancelling

I usually have a panel of 3 guests on the show, and it’s common that within an hour before we record, someone emails with an emergency and is unable to join. How often does this happen to others? I’m at the point where if I still have 2 of 3, I don’t reschedule. But still really frustrating. With enough notice, I find another guest, and life goes on. But an hour in advance is hard!