You never try to do a belly landing (i.e. landing without landing gear down) in an airliner. Gear struts are attached to hardened point on the most strengthened airframe structure.
So if you're in doubt if you can make it to the RWY or not, DON'T retract the gear.
When you crash land with the gear down, part of your impact energy is taken away by the gear, so less force against the rest of the airframe.
If you crash land without the gear, all impact energy goes into the fuselage, this cracks and brakes up, as we have seen so many time.
Dani