A Japanese wedding invitation comes with a reply card. A guest who cannot attend marks the card for absence and adds a short reason.
If the real reason is a death in the family, wedding guides advise against writing it. The guest writes tsugō ga tsukazu, it could not be arranged, or yamu o enai jijō ni yori, due to unavoidable circumstances. One guide says that the right answer is to keep it thoroughly vague. The real reason can be told later, by telephone.