Currently there are two settings for MUC persistence, forever and until it everyone leaves. Having your room destroyed because you had a network hickup seems annoying. Having rooms exist until long after all its users have left seems like wasteful. As a middle ground, persistence could be a time to live since last activity, with a few presets like a day, week, month etc. This way, admins can restrict who can create infinitely persistent rooms while still avoiding some of the problems of presence based persistence.

lovetox suggests making persistence be exclusively an operator setting, no room config option.