On a air/ oil cooled ATV the ATV will go hundreds of miles with a broken fan and muddy oil cooler rad.
On a liquid cooled ATV if the fan quit or the rad was muddy it would not go much more then 100 yards before boiling over.

My old 89 Big Bear's oil cooler did not even have a fan . My 87 250 Moto4 did not even have a oil cooler period.
Both still running to this day BTW.

My Sportsman over heated 3 times , once for a fan that died, then for a thermal switch quitting that tells the fan to turn on and off and then once because of a air lock in the coolant system.

 

a liquid cooled engine should last longer in theory, but that's as long as the radiator and other components don't fail you. seeing as many old air cooled quads are still running good I don't think its a big difference