Two observations:
1) It's difficult to get people to stick around for fights that aren't lopsided in their favor
2) Characters that play a balls-to-the-wall style, eating and dishing out deaths with seeming disregard for their own well-being, are fun to have around as friends or as enemies

One suggestion:

I'm thinking of something similar to the way morale works, only call it "bravery" or the like. The broad idea is to create incentives for good behavior and dis-incentives for bad.

You gain "bravery" by doing things that fit with the second observation above. Winning a PK fight, dying in PK, defending a cabal, raiding a cabal, etc. You loose "bravery" by the opposite: wording out combat, teleporting while adrenaline is pumping, fleeing from combat, not showing at your cabal when there's a raid, etc. There may be no negative affects, just movements back toward zero. There might also be pressure over time moving it back to zero if you don't actively keep it up.

The affects should be noteworthy and visible: for example, when your "bravery" is high melee classes gain damage while others gain hps, and the stat shows up in your affects as a -1 duration item. Or maybe what you gain is random for every bravery "threshold" you cross, but always class-appropriate.

The real point of this is to add costs to legitimate but undesirable activity that is currently costless, such as fleeing and quaffing as soon as you're attacked. Nothing here would prevent you from doing it, but it at least offers some reason to consider taking risk instead, especially if dying in PK adds to your bravery.

Dying in a pk isn't brave really. A lot of time it is stupidity. You don't win wars by dying for your cause, you win by making your enemies die for theirs.

I'm all for a little bump or something to help out victims that die all the time, but anything else is silly and distorts what bravery is.
Since when is it desirable to let yourself be killed when you have a means of survival? Who would really stand and fight in a 10% chance of winning when they have a 95% chance of escape. Better to flee and start evening the odds some for your inevitable next encounter once you get away.

People take calculated risks all the time. Most vets are so adept at situational pk that they know the correct choice between fight and flight in almost every scenario and can make it upon being attacked. Most will fight if they are at around at least 40-50% chance of winning (or have some other reward/rp reason to go for it such as raids or keeping group mates alive or whatever). Adding a perk to guys that run around exploiting the advantage they have as the initiator of a pk does not make a lot of sense, since in most all scenarios outside of retrievals, the guy attacking has an overwhelming advantage in a pk scenario. And the last thing I want to see incentivized in any way is no rp murder alls.

I think adding any sort of perk to pk winning is really just stacking odds against a newbie.
Now a perk to dying is not such a bad thing to imagine if it softens the blow a little.
But I think it would have to make sense from a mechanical and RP standpoint.

I can think of situations where being brave requires fleeing from combat or wording.

Also there is a cost to fleeing and quaffing.
Teleport - You could land in a locked room with an angry mob or a series of angry mobs. At hero range this is less of a factor but still a drawback.
Word of Recall - Halves your movement and puts you in a known location--one of the hometown locations. Which really narrows an agressor's search for a short period of time.

I want to point out that a newbie who has potions is likely to flee and quaff right after combat. Or a vet that was not ready.