Not sure how this one is going to go over, but here it goes.
I've been engaged in this hobby for more than 20 years now. I have seen and played every edition of D&D there has been pretty much. For most of that time, it has been my priviledge to be the DM for the various groups with whom I have played. Over those two decades I have learned one very important thing:
There's rules, and then there's more rules, and then there's common sense, and then there's the story.
As a long-time gamer and game designer, I know that there will always be situations that crop up that the designer has not and cannot anticipate. Even if they can anticipate them, they can't necessarily write the rules for them: if the designer's try to take into account every single permutation than the rulebook would become prohibitively huge.
During my tenure as DM, I have learned that as artifical constructs designed to facilitate gameplay, rules are sometimes unable to take into account logic and reality, especially during combat situations. Realistic combat cannot be achieved using the standard D&D rules. I recall only one game system that tried to represent realistic combat, and the entire game would bog down once combat began. D&D combat is really quite simplified and abstract in nature. This has been done to speed up combat situations.
Common sense often wins out in games that I run. If the rules don't cover the situation, or the rules that do cover similar situations cannot logically be applied, than I go with logic over rules.
When it comes to telling the story in which the PCs find themselves, I can, will, and have thrown the rule books out the window if they interfere with what it is I'm trying to do.
I have only ever caused the demise of a handful of PCs over the years. I cringe every time it happens. I had to do it recently, but that was only due to the actions of the PCs and not anything I had planned or done. There are times that I go out of my way not to kill a PC. If letting a wounded PC escape from a situation as outlined above does nothing to harm the plotline, and does everything to help keep the player's precious PC alive, than my ruling would have been easy: Let the PC escape.
I know, not as rules heavy as other responses, but more usable.