I'll concede on the "serious bodily injury". You stated that much clearer than I did.
However, in PA, you may carry and drink at the same time. Not sure about how many other states are the same, for I know in OH, you cannot even carry in a restaurant that serves alcohol. However, with that said, someone who was drinking and does shoot, will be looking down a prosecutor's line of questioning that will get very intense. That prosecutor will try to rip his judgment apart and state that the alcohol in his system played a role in bad judgment. This could discredit an otherwise credible justified shooting. Regardless of the law in the state, drinking while carrying is a rather stupid thing to do.
Again, as you stated it comes down to the state the attack happened in, and we need many more details as to what happened.
And to CharlesMorrison, excellent point. How is it a firearm's instructor does not know when to employ lethal force? I howled when I saw what you wrote and then shuddered a bit knowing there are firearms instructors who are ignorant of such things. I'm hoping the OP just wanted our thoughts, but now I'm curious.