Disappointment

I received some disappointing news a while ago that Mr. Snowflake's mom, sister and her husband, maternal grandparents, and other family members from that side are not coming to our wedding. She's been flaky about our wedding for a while, but I didn't actually think she'd decide not to come and completely remove herself from the process. I'm just really disappointed. Let me back up and explain how this all came about. Mr. S's parents were divorced when he was a teenager and it was a really messy divorce. There was a lot of fighting between FMIL and Mr. S's dads side of the family, that eventually escalated to FMIL getting slapped by Mr. S's aunt. So basically FMIL and FSIL have not spoken to that side of the family in about 16 years. When FSIL got married two years ago, no one on that side was invited. Mr. S has always been the bridge, he's friendly with both sides. When we have any holidays or b-days, we have to do everything twice.
When Mr. S's dad passed away 6 years ago, it drove another rift in the relationship because Mr. S inherited money and FSIL did not (they had not spoken in several years and refused to come and see him before he died). Anyway, FSIL and FMIL thought it was wrong and have always given Mr. S a hard time about it. Even this Christmas when we begged to celebrate X-mas at our house, FMIL gave us a hard time, we thought it was perfect because we have a bigger space for everyone and then since we're the ones with kids, we wouldn't have to lug all of the toys home. FMIL kept insisting it would make FSIL uncomfortable because of the money (which was not much and we have a seriously large mortgage - actually we have three mortgages with our three houses). In the end he confronted his sister and she said she had said nothing about being uncomfortable and thought it was a great idea, so we got Christmas at our house.
When Mr. S got married before his mother came for the ceremony and then took off. Now that we have the kids, I figured she'd come to support Mr. S and to hang out with the kids. I would have totally kept the families separate to make her comfortable. We would have had our friends run interference all weekend (confidentially of course). We've even had some of his aunts and uncle's from his mom's side RSVP, will they pull out now? His dad's side of the family has asked no questions whatsoever about his mom coming and they've been super supportive of the whole wedding, I'm sure they're just assuming she'll come and they'll be civil. They know that my FH will not put up with any drama at our wedding.
I know that her reason for coming is not my fault in any way, she is just still not over the events that happened in the past. Mr. S says it doesn't bother him that she's not coming, but I still can't help but feel really bad about the situation. I'm still going to send an invitation and continue to encourage her to come, we'll see what happens. I think she'll really regret it later if she doesn't, but I guess I could be wrong too.
(Us with FMIL at FSIL wedding)
Have you had any disappointments with family members you thought would come and then didn't?