So they need to be prepared. I agree that it's a very difficult situation...to read and respond to. It's acknowleged that this is a really difficult area for cops and many depts are working on better education to read the signs better. But sometimes, lethal threat is a lethal threat, mentally ill or not.
In a similar case here a few yrs ago, after investigation, the officer was fired but they (considered but) ended up not bringing criminal charges.
I am not saying that lethal force was required, IMO, in the OP incident however.