Leaking water can sometimes create a massive water blister in latex paint on a ceiling. You may mistake this for ruined drywall when, in fact, the drywall may not have to be replaced.
Prick the large blister and let all water drain out. The day after the leak, test with your finger to see how stiff the drywall is. If it's solid, you may just have to repaint and not replace the drywall.
The key is to minimize the amount of water that saturates the drywall. I've seen many a drywall ceiling that dries out and survives. It's not unusual at all.
If you're worried that the drywall might fall from the ceiling at a later date, you can always install additional screws. If you have 1/2-inch-thick drywall, then use 1 1/4-inch coarse-thread screws. Be sure the drywall screw is countersunk about 1/16 inch. If you go any further, you will tear the paper around the bugle-head screw, rendering it ineffective.