I do not agree that he could face negligent homicide charges.
One first has to demonstrate negligence. If the other hunter was the one who got out of line, then he was the negligent one and not Cheney.
Every friendly fire incident has someone who has turned up where they ought not be. The question is "who?"
If he dies and if Cheney is found to be negligent, then he would have to answer to the charge of negligent homicide. In his statement today he has as much as admitted to negligence. He says he didn't see him, but then when you have a gun in your hand that really isn't an excuse. He had a duty to ensure that when he pulled the trigger that there were no people in his sight. He breached that duty, hence he was obviously negligent. This is one of those "res ipsa loquitur" situations (the thing speaks for itself."
I doubt there would be a felony charge here since there was no reckless disregard for human life, but I don't see how Cheny can avoid a misdemeanor involuntary manslaughter charge. Any of us would have to face such a charge. Cheney should not be exempt.
That being said, this is a tempest in a teapot. Something akin to crashing your car because you were looking at your cell phone.