Re: What to do if a shroud or stay breaks
The idea is that you want to change your point of sail to relieve the pressure from the broken rigging. So, if you're on a starboard tack and the starboard shroud breaks, as quickly as possible you go to a port tack. If you're running downwind and the backstay lets go then you head up into the wind as quickly as possible. On any particular point of sail there will be some part of the rigging that is taking the majority of the strain, and some part that is more or less loose. Shift the point of sail so that the broken stay is one of the loose ones.
Of course, like SlowButSteady said, there's a good chance the mast is going to come down anyway.