Very simple. Keep the 24 hour restrictions as-is, but allow transition to an offline mode after notifying the mothership. This disallows all the family sharing features. Games installed using a physical disk would require the disk to be present, downloaded games are unaffected (since you can't sell them without connecting to xbox live.) This takes care of the submarine scenario. When you're back online, check for the disk again before allowing disk-less play. Make sure the offline transition can be done through smartglass, and you handle the hurricane/somebody-cut-the-fiber scenario as well.
Any holes in this approach?