An MMO of sorts which is essentially Planetside but Chivalry; You have your crossbows and swords, horses and catapults, and everything. You are broken down into ranks and files in a feudal power structure of sorts.
Most importantly, you only get one life per battle, and you don't so much resurrect as get replaced by a family member. You'll have the same family crest and (perhaps) some attributes you've gained by leveling up your "family honor".
The low-level game is a tough ground-level slog; low-level characters lose very little with each death, while high-level ones lose much more. Since commanders will be higher level, they tend to avoid direct combat, which somehow seems realistic to me.
There's plenty of tweaks to that, which I will mostly skip over for brievity. Suffice it to say, I'm sure some "deaths" could merely be being subdued, allowing comrades to recover you. Nobility/high level could be a long-term boost for your house, although a death could still demote you from Baron to Knight, Heir to the late Baron.
Importantly, actual leadership is not a skill or attribute, even one of nobility; you are given leadership positions by a higher-ranking member of your faction, and that includes the ability to give orders to lower-ranking members (and dispense new leadership positions, naturally.)
This is all you need for the basic idea, which is an online ad-hoc-sword-based-surgery-simulator. However, this is missing an important part: Backstabbing.
As you get higher ranks, such as that of Count, you can start observing the (mostly self-managing) economy, and you can be aware of good harvests (plentiful food means that people are cheaper to replace), caravans of gold entering the region (GOLD!), a plauge amongst horses (weakening mounted units...). And you can see the benefit when the Franks offer to grant you food for your starving County in exchange for, well, not to put too fine a point on it, but changing sides.
At which point, you can switch sides, and tell you men to switch sides! And if one of your lieutenants is a filthy loyalist, put a price on his hide! Perhaps he'll go outlaw, perhaps he'll try to reach the border... you don't know, because he is a human player as well!
Marry your cousins off to great generals (effectively, decrease your family's power and increase theirs)! Send a caravan of rare metals to a major city (under armed guard... which might not be entirely trustable...) in the hopes that the engineer there will invent a better steel! Maybe even hire a boat to take a spy to an enemy port under cover of normal trade traffic...