I have not been able to die while knocked out due to blood loss. I have tried to bleed out several times now. Every time I run up to a zombie and let it hit me a few times, I kill it and walk away until I passout, which happens in short order. Once I pass out, I just lay on the ground bleeding until I click respawn. Last time I tried, I waited some 20 minutes. I will try to wait a whole hour next time to see if I am just bleeding slowly.

Update: Replicated same bug, I have now been unconscious for 100+ minutes and still have not died from bloodloss. Not sure if bleeding is broken or immortal.