The sovereigns death costs 50% of their mana. It can hurt a lot If you really want to kill him, freeze him in place for 10 turns and use Curgens volcano on him. 

As for heroes, I think the design is a bit silly that they "retreat" to the nearest city and can fight again, just to get more injured. They should be locked out of the fight or transported to the capital instead. 

This has been something that has bothered me for a while as well.  If I had my druthers I would make it so that only the Sov can retreat and gains an injury and loses a set amount of mana not half.  50% can be a very extreme loss later in the game whereas a set amount can hurt initially but the injury might not whereas later in the game accumulated injuries would make your sov much weaker.  I liked the Heavenfall had a compromise in one of his mods that when a champion accumulated injuries you had a chance to permanently die from future injuries. 

That is why I said the best solution so far was for champions/sovs accumulate injuries that can eventually lead to death if not removed.  Unlimited deaths is somewhat silly but knowing that as your champ/sov dies it becomes more likely it will be a permanent loss so you will be more careful with them.

A huge problem with dying heroes was that so much of your magic power is dependant on successfully leveling them up. If heroes were to risk dying just to be stronger mages, that is a large disincentive to go for magic.

Sorry for the back to back postings. but maybe the world difficulty could scale the % a hero has the chance to die. i think heroes would need to be slightly more powerful to balance this out and make them worth using even with the chance of perm death. i believe frogboy posted somewhere saying this was more on how you build your empire/kingdom rather than your tactics that ultimately determine your victory. it would just be nice to know that how i engage each battle can make a huge diferance in the end. thats the reason i love games like this. its the tacticle battles and taking a group of weaker units and defeating a powerful foe just with superior tactics.

The other problem is that this game will sometimes just throw your heroes under a bus.  i.e. chucking your mage in the frontline when you are fighting 3-4 plaguestalkers/assassin demons.

You would need some type of deployment system and probably also a retreat option (at the cost of mana) but that is basically what injuries are anyway - they are a retreat option with a slightly different label.

I dont like this fact too. My heroes usually dont die, i take care of them. Next fact i dont like, you dont get the equipment of killed champions, even if this was thier last death ... they grinding the area and looting MY! treasure ^^ but i cant get it back

Champion death should be permanent but then they need a little HP-Boost. Sovereign should get injuries on death and a 10% Mana loss. After 5 unhealed injuries you lose the game through a dead sovereign and dynasties would be a great goodie i think, like in the original Elemental game.

Crusader Kings is a great game, isn't it?

The problem with permadeath in WoM/FE was that champion recruitment was basically random.  You might have a dozen in a game or two, depending on how the map generated.  If you have a dozen champions and one dies, no big deal.  But if you have 2 champions and one dies, the game is over.  Champion death just exacerbated the lopsided nature of those games.

I think with the new recruitment mechanic in LH, you could have permadeath without too much pain.  I wonder if the game would support a mod that gave champions could have a high chance of permadeath (say 20-30% each time they fall in battle), but if they die you get a new champion selection screen.

noted. seems it is split on perm death. heroes should be the symbol of power in your army but making them mortal would not make it easier to steam roll another faction. because you heroes would be mortal as well. if your enimy snipes your hero you'd feel it in the long run. just like if you wiped out their main stack. 

You could also have difficulty level affect this. So at the highest difficulty levels, your champions will die after maybe two injuries.