I agree, I suggested this before. It makes sense for me for a lord/companion/ and PLAYER to have deep wounds after falling in battle, needing rest to recover. The solution is so simple, start death chance of every significant NPC at 0%, then after falling in battle he gets a WOUNDED status (if not enough time passes/if the player or npc doesn't rest enough so that the wounds heal then this death chance goes UP to 2% or 5%, so next time he falls in battle he has a serious chance of death (also if the lord/companion is IMPRISONED that time doesn't count as "resting"). If he survives falling in battle again then this chance goes up even further. That way reckless lords will die more often and cautious lords would survive longer, as it makes sense. Same for the player, good cautious players will live longer, giving the game a WELL NEEDED challenge and consequences (so it's not totally BORING, because please take note that GOOD players will barely lose ANY battles in their campaigns, the game is not hard at all. We are talking about players that have mastered masterpieces likes the Prophesy of Pendor mod in Warband and such, which was one of the more challenging ones, which also made it the most fun).
Also times of peace will actually mean a damn, because it can save lords from dying, and it can give the AI another reason to propose peace ("we are in danger of being overrun/our lords are wounded and tired" etc).
This is the absolute best way to implement this imo, I don't know why it's not taken into consideration already... Deaths should be more rare and feel more significant, and feel like they can be avoided for the player and his companions, and it not being just a simple dice roll. If you want to go even more in-depth the type of armor you're wearing should also reduce deep wounds chance (heavy armor is less chances for being wounded etc, you can make this chance something like: 70% chance to be deeply wounded after falling in battle for light armor, 50% for medium armor, and only 30% for heavy armor). This can also make armor feel more significant, and make the penalties to movement speed actually worth it. Low tier clan leaders would have lighter armor than high tier clan leaders, so this makes for a system where the top dogs that have more economy etc actually have more survivability as a whole, making gameplay a lot more dynamic so that low tier lords die more often and high tier clan lords are more hardy and you can actually remember them throughout your campaign more because their presence is consistent and they're not replaced every year.
@Dejan if you could please forward to the devs ideas like this, I think such ideas could make the game a ton better. It's more in-depth but not too complicated. Players would 100% love it in comparison to a simple death chance you have no control over, I'm 100% sure of that, I promise you.