Can we just do the destroy/rebuild for them automatically when they change the event?

Oh I guess that wouldn't work either if people linked to events.

Yeah, and the worst case would be if E111/4 is actually E112, an exception, and E111 gets auto-converted to E222. Then E111/4, also known as E112, will no longer be part of the E222 sequence. We could start keeping track of the relationships, but that seems like a lot of work with little pay off and possibly way more confusion.

An alternative philosophy, which has been adopted by Google calendar, is simply warn users that changes to a recurring event will destroy any exceptions. This seems less reasonable in a shared calendar.