FWIW I have rescheduled plenty of birthdays in order to make it the best day possible. I don't think at 4yo he's going to care if 'his day' is on Monday or Tuesday - kwim? Maybe you could find a middle ground and get the day you planned, and your husband protects his recovery, by just doing it a different day?
I do understand the loss (not quite the right word but not coming up with any better right now) to you though - that once again alcohol/AA is coming first. The long term pay off is worth it but that doesn't mean the sacrifices you make aren't, well - sacrifices.
