The full breakdown for damage is:
Code:
Damage Prob Result
2 2.8% No Injury
3 5.6% 4 HP, HT+0 check vs Stun
4 8.3% 8 HP, HT-10 check vs Stun
5 11.1% 12 HP, as above plus HT check to stay conscious each round*
6 13.9% 16 HP, as above
7 16.7% 20 HP, as above plus HT check to survive
8 13.9% 24 HP, as above
9 11.1% 28 HP, as above
10 8.3% 32 HP, as above plus 2nd HT check to survive
11 5.6% 36 HP, as above
12 2.8% 40 HP, as above plus 3rd HT check to survive
*I think this is at -1 at -1xHP, -2 at -2xHP, etc, but I'm not certain
Staying conscious requires either succeeding at the check vs stun or failing by less than 5. This is a given for 2 damage, requires a roll of 14 or less for 3 damage, and requires a roll of 3 or 4 (Critical Success) for 4 damage or more. That's 0.028 (1*0.028) + 0.051 (0.9074*0.056) + 0.017 (0.0185*0.916), or about a 9.6% chance of remaining conscious, not even considering the 50% (or less) chance of staying conscious each additional round 83.3% of the time (5 damage or higher).
As for survival, that's a given (ignoring bleeding) between 2 and 6 HP, requires one roll of 10 or less between 7 and 9 HP, two rolls between 10 and 11, and 3 rolls at 12. Probability of survival is thus 0.583 (1*0.583) + 0.21 (0.5*0.417) + 0.035 (0.5*0.5*0.139) + 0.0035 (0.5*0.5*0.5*0.028), or about an 83% probability of survival.
So, less than 10% chance of staying awake, but 83% chance to not die outright. Both are probably higher than is realistic, of course, but at least the first isn't terribly off, and the second plummets when bleeding rules are used.