Falling off the tower killed Ansom, a level 10 Chief Warlord, but not Bogroll, a twoll. Did the fall strike less than 12 hits from Bogroll, or could Regeneration raise him back from 0? (And being burned, as he was, was the only thing that could kill him?) The twoll in the forest was not burned. Perhaps Ansom died first, and the ensuing 2 levels gave Bogroll enough additional hits to survive?
Perhaps the source of defence is important. Ansom's was derived at least partially by armour, which would be a hindrance on landing, whereas Bogroll seems to not wear armour, suggesting his thick skin is providing the defence value. Or possibly Bogroll had a soft landing on Ansom's (very recently) croaked corpse.