So sorry to hear that this has been stressful on you and the FI.
It's always the important moments in life that allow to see who are your real friends and who really cares about spending your special day with you. It's understandable if someone cannot make it to your wedding due to scheduling conflicts or money issues. But he'll be on vacation the week of your wedding. That, i'm sorry, I don't understand.
Oh well, what's done is done. No need to sweat it anymore. Just remember, your day will be perfect cause you'll be with the man of your dreams.
Feel better and let us know of any progress you make in this situation. Good Luck!