How much damage could a landing gear malfunction do?
According to Belly landing:


  During a belly landing, there is normally extensive damage to the airplane. Belly landings carry the risk that the aircraft may flip over, disintegrate, or catch fire if it lands too fast or too hard. Extreme precision is needed to ensure that the plane lands as straight and level as possible while maintaining enough airspeed to maintain control. Strong crosswinds, low visibility, damage to the airplane, or unresponsive instruments or controls greatly increase the danger of performing a belly landing. Still, belly landings are one of the most common types of aircraft accidents, and are normally not fatal if executed carefully.


It is possible that the friction from a belly landing could wear a hole through the underside of the fuselage. However, even if this were to happen, airliners carry the passengers and crew in the upper half of the fuselage, so nobody would be likely to notice (from inside the aircraft before emergency evacuation).