I think its good as it is. You have 1 chance, and thats it. Orelse you can steal bandages from dead people.
The idea with ambulance is kinda intresting, but i think it would move the focus away from strategical realistic playing of a battle, and make a "healing-unit" like in WoW or something. The ambulances didnt really heal anyone, they just drove them away from the battle. I say the FH2 maps represent a short battle, maybe just a firefight, where no healing or bandages really would help you before earliest the next day.