Well, I guess that's up to you. HP is convenient in that it's an easily balanced factor and you don't have to worry about implementing things like blood supply, bone/joint structure, nervous tissue, etc. Honestly, if you weren't planning on expanding it past your generic humanoid (maybe with a few species besides human for variety), you could keep with a less challenging state-oriented design and drive it with some much less generic programming. It's obvious to us what happens if a foot gets cut off - DF does it procedurally because it has things with more than two feet, things with no feet, things that fly, things that don't feel pain, etc. etc. The variety makes it simpler to actually define how those things work with each other and let the game take care of the falling-down-or-not part. For this, it would be complete overkill (albeit fun simulation-madness overkill)
For the combat, I was thinking a simple tradeoff - you can do none, one or both of magic and fighting. If you focus on one, you get better results but you run the risk of not having a counter available to a potentially fatal maneuver for that type. Counters could be done automatically, using skills you pick alongside your regular fighty/heart-stoppy skills, with another trade-off between effectiveness and speed. Meaning you can reverse a spell on someone, or drain it into your reserves, or other special things if you didn't use magic that turn, but you could only do a simple shield spell if you had been fighting, and you're SOL if you fought and used a spell on the same turn, unless the maneuvers themselves somehow disrupt your opponent's efforts or your opponent is incapacitated.
The whole trading blows until someone falls over and dies is just a little old. I'd like to see more stuff where you or your opponent can die on the first turn if you're reckless, much like a real fight. Also, wizard lightning! In real life, wizard lightning is a lot more dangerous, right?