Heroic Luck wouldn't necessarily make a hero unkillable. After all, there's no reason why it'd have to increase linearly and unbounded, rather than asymptotically approaching some sub-100% upper bound. And even if it did reach 100%... that's nothing that Umor can't handle.
(and one might consider perhaps cons6 or cons8 items to weaken luck).
On a related note, it strikes me that it would be useful if a modder could give constraints or hints as to what HoF ability would be given to a specific hero. In fact, for a veteran hero (say, an already legendary one) -- it would make sense to assign both XP and a specific HoF ability (but one which wouldn't increase further unless he remained within the HoF).
For 'neophytes with potential' heroes, constraining HoF ability choice would lower the risk of getting something wildly athematic. For instance, it would be galling for Heroic Stupidity to land on your average heroic sorceror-type, and Unequaled Obesity might not make sense against a backstory describing feats of long-distance running, et al. A great paladin champion and enemy of the undead shouldn't suddenly get Undead General. For a healer-type to get Legendary Cruelty would be rather bizarre, unless she's got a rather odd personality or doubles as an inquisitor... I don't know if the game would ever be perverse enough to assign such, but the ability to give hints to the engine would help.
HoF abilities
Hybrid Mode
