I feel that given that it's possible to kill/maim with bare hands and/or a convenient rock/stick, the attacker, by threatening to do the victim bodily harm, has already escalated the threat to a level that should allow the victim to use deadly force to protect himself - the victim shouldn't have to wait until he's on the ground struggling to remain concious to decide "OK, I think my life is in danger now, it's time to pull out the gun."

With regard to this specific case, if Kuenzli did indeed charge at Fish threatening bodily harm after Fish had already fired a warning shot, it demonstrates a disregard for his own life that puts Fish in that much more danger.
As far as other options were available - my question is what other options do the prosecutors have in mind? Let's see: Fish can 1) do nothing and wait and see if he's going to be beaten senseless, or 2) he can run back up the trail he's just exited, resulting in either having to make the same decision when Kuenzli catches up to him or Kuenzli and his dogs between him & civilization, 3) whip out his cell phone and hope he has time to call 911 and hope the police arrive before he's killed, or 4) he can wait until he's reasonably certain he's being attacked and fire 3 shots at close range into the chest of his attacker. Does anyone see any other possibilities here?