idealistically the 0% of stamina that our gui shows is not that of total exhaustion to the point of collapse, but actually the highest amount our body can withstand before feeling immense strain or lack of energy to possible continue tasks at a constant speed/rate
ie, you run your ass off for 100 meters, then have to slow to a walk to catch your breath, thats your stamina gone, but you don't collapse... well, not unless you're very unhealthy :]
it is a good idea indeed, but perhaps after the main stamina bar there would be that reserve 'danger' bar, or a negative amount, kind of like Moons idea (was it moon? with the -45% = total death) the further into the negatioves your emergency stamina goes the closer to collapse you get, and then if you managed to push it to such a far point, unconciousness.
typos fixed.. I need to stop hitting ; instead of ' ><
edit: there are many things like fainting that would be ever so helpful for RP, I'd love to see faint and several others, but it's getting the animations and such thats tricky :s