He's not a real person, and the situations he's placed in are far from real.
The question itself is utterly ridiculous, because he's a character in a bunch of stories which usually have no moral questioning. To then throw him into a situation which is well outside the possible world he inhabits is the stupid part. You may have well have asked "If it were a kill or be killed situation, how do you think Mickey Mouse would go down? Would he kill, or would he go down fighting?" such a situation can never happen in a Mickey Mouse story, nor can it happen in a Batman story, because neither can function in the context of real-world moral dilemmas.
Its a stupid question.
No matter how often I've read that line of thought, it never cease to be annoying and completely besides the point. Here's a guy who's obviously a fan and as such, has some level of emotional investment in the characters and you somehow felt the need to piss all over him for asking a question .
Get over yourself man!
In what way was it clearly not a kill shot besides wishful thinking? The guy says something like, "Stay back, I'll kill him, I'll kill him" and BANG and then Bats says, "I believe you." There is a single frame in which you can't quite make out where the bullet hole is, but the back wall is covered in blood. Then the next scene we have Batman is interrogating the third mutant. We never hear about the one he shot ever again. There's absolutely no reason to believe Batman would have shot to injure, given the context of the situation, the child's life at risk, his characterisation thus far in the story, etc. If he HAD shot to injure, he would be intentionally choosing the action which would be more of a risk to the child, so how can you defend that decision?
How a
Seriously, there's no reason presented in the story to believe that Batman hasn't killed that guy as the last resort. Besides the fact that Miller originally wrote DKR as out of continuity, and therefore to do whatever he wants, why assume that Batman's ridiculous oath to never ever take a life applies?