POD to the fact that things may not turn out exactly the way you think, but don't get upset about it.
A good friend went to a wedding where things went wrong in a major way. Everyone was sitting in the dining room of the hotel where the wedding was being held. Starters had just been served when the fire alarms started ringing. It turned out that there was a fire in the kitchen. A big fire. Everyone was evacuated and the Fire Service turned up to deal with the fire. There was a lot of running around on the part of MoH, BM, HC and hotel management about what to do about the wedding party/food etc. Another hotel and a nearby restaurant were contacted and were able to supply food for the rest of the dinner, and luckily it was a nice evening, so tables were set up quickly in the gardens.
Yes, things were delayed, and the dinner/decorations weren't as planned except for the first part of the evening. However, in the long run? The HC are proud of their extra wedding photos with the fire engines; all the guests say it was the most memorable wedding they have ever attended; and the three businesses involved have had huge numbers of recommendations due to the way they handled a difficult situation - the original hotel for calmly managing to organise a solution despite not having a working kitchen or dining room and the other two for stepping in to help with an emergency.
OK. I know that most weddings don't have such major problems, and I sincerely hope your friends don't. However, I thought this story would illustrate how even the most horrible problems can turn out well in the end.