Well it's not really a huge "issue" for the wedding but FI talked to one of his GM today (because he hasn't gotten fitted for his tux and hasn't sent his RSVP) and was told that he might not be able to make it because he might not able to travel from his base (he's in the military). I don't really know any details.
It's no biggie for the wedding if he can't come because I don't mind if the wedding party is uneven. It will just stink if he can't make it because he is one of FI's oldest friends and I know he would really like him to come. I've never even met him and I was looking forward to it so I hope he can make it!