I would say it really depends where it is bleeding from.
If the fish is injured in the gills and it's just pumping out blood with every respiration, then chances are it's a goner. That blood that flows through the gills attach oxygen before returning to deliver that O2 to the rest of the body. If it just leaves the body and enters the water, the fish is gradually getting less and less O2 and will eventually go into a state of shock / death.
Fish hooked in the jaw area and are bleeding usually survive in my opinion... even if a whole chunk of skin/flesh is ripped off. We've all caught fish that have been caught before with visible scarring. The bleeding tends to eventually stop after the blood coagulates. Healing is a very quick process, given good conditions. If water quality is bad, then fungal and bacterial infections do occur and can be fatal. I've seen fish with patches of fungus over their bodies in different lakes/ponds etc. Once an infection takes hold, it spreads rather quickly to other areas of the fish.
I'm unsure of this, but in my experience, fish blood tends to coagulate (go from liquid to a solid state -- blood clotting) rather quickly. Maybe there is a some kind of reaction with water that causes the blood to clot and stop bleeding. The blood must clot quickly especially in an aquatic environment.