Can't find a link to the story right now but this happened at base in Iraq or Afghanistan. MP was instructed to fire a warning shot at truck that didn't look like it was going to stop for the gate but the MP shot and killed the driver instead. I can't remember if the truck blew up or if they found the explosives in it when they searched it after the drivers death but either way if the MP hadn't killed the guy they would have had a truck bombing in the base or at the actual gate.
I'm certain the military killing of a guy with a warning shot that was investigated by the military was as the military states actually a good thing, and a happy miracle.
Also, no, it wouldn't have. If they ignore the warning shot, the next shot isn't a warning. They don't let the guy get into the base, they don't let them approach the gate, they don't approach the truck until the operators are out, they aren't dumb. The military has procedures for this and when a warning shot is applicable, they have ample oportunity for a kill shot afterwards