I think there are rules for catching yourself if you fail a climb check...
I would say reflex to grab the ledge, strength check to hold on. Failing the strength check means you grab the ledge but can't hold on, but you lessen the damage by slowing yourself down. Success on both checks = no damage. I see no reason to try to be more realistic than Die Hard in a world where it is easily possible to:
see the future,
ride/fight dragons,
raise armies of undead,
teleport to anywhere,
go to different dimensions,
create stuff out of thin air,
kill gods,
etc.