There has to be some ceiling joists that the interior liner is glued to. If the liner has dropped, look to see if it's damp up there. Remove vents / speakers to feel above the liner to see. If it's wet, assess how bad the damage is. Fix the leak, likely pull the ceiling down, fix the damage, put fresh materials back, rebuild the liner. Lot o work...
2002 Newmar Mountain Aire Limited 4370 w/ Spartan K2 and Cummins 500hp
ASE Master Certified (a long.....time ago...)