I recently got married. Although we had a small wedding we did send out proper invitations.
With the exception of one couple, everyone sent a card responding. Having waited until we had to confirm number of attendees with the venue, I followed up to see if they were coming. They said they would come to part of the day - OK no problem on our side.
But then on the day they just didn't turn up. No call, no text, nothing at all. And nothing afterwards either until 3 weeks later DH gets an email to ask if we are back from honeymoon because it would be great to catch up.
No apology, no card, no best wishes, no hoping we had a lovely day.
Personally I would just cross them off the friend list but wwyd? I have been friends with them for over 10 years.