Has anyone but the OP actually verified this is even true? (I'm not saying it isn't, mind you.)
It can't hurt to ask about an exchange, but it is unlikely that you will get it. I can understand being disappointed, but the show is really wonderful, that I'm sure you won't feel you've missed anything. (Is it really going to be Tovah? I'd love to see that!)
As far as others being out...no guarantee on that either. They can't very well tell the rest of the cast that no other vacations will be granted during the entire month. And of course, illness or injury can also come into play. For example, I can't see Terrence Mann and Charlotte D'Amboise not being granted vacation together.
I say, just go and enjoy the show. If its REALLY any good (and I think it is) it will be wonderful even with replacements and understudies.
If we're not having fun, then why are we doing it?
These are DISCUSSION boards, not mutual admiration boards. Discussion only occurs when we are willing to hear what others are thinking, regardless of whether it is alignment to our own thoughts.