A runway used by a C172 and is, say 2000 ft long will suffice at low altitudes, however, this runway will not accomodate a heavy passenger aircraft and, certainly not, when the brakes or tire friction fail. So it boils down to common sense used by the pilots, although this is questionable as the Air France runway overrun in Toronto had more than enough runway length, but the pilot decided to stay on the deck even after he had landed long because of an (non-stabilized approach) overspeed situation.
Having a cliff at the end of a relatively short runway overrun puts weight and performance restrictions on aircraft and, again, the pilot has to use common sense in rejecting its use when he knows that a slight miscalculation of runway friction or temp/alt effect on engine performance is highly probable. This can all be determined and decided long before actually using the runway.
Experienced pilots who value their lifes will make the right decisions.
