My question involves criminal law for the state of: OR
This situation happened to a 'friend' of mine recently. He had a not-so-stable girlfriend with a history of self harm and mental illness, and wanted to break off the relationship so he told her he was leaving her. She proceeded to immediately grab a knife and slash her wrist, drawing significant blood, while exclaiming 'then i'll kill myself' (witnesses in nearby apartment heard this). Then she continued to make allegedly threatening gestures with the knife by holding the knife vertically in the air, and this apparently left my friend in fear for not only her safety, but his own (even though no explicit verbal threat was made against him). He's a pretty knowledgeable guy and he knew there are several laws protecting a person's personal bodily autonomy (i.e. simple assault/unlawful restraint), but he was also in fear that if he just sat there or left the unit altogether, and let her continue to harm herself, possibly even kill herself, that he could also be held morally and legally responsible (i.e. something along the lines of involuntary manslaughter).
The struggle happened so fast, and persisted without pause for so long that he did not have time to find his cell phone and call the police. He also feared that calling the police would only provoke her further, possibly jeopardizing either his or her safety further, and land himself with an arrest regardless. I won't go into detail about how the rest of situation went, but it didn't work out so good for my friend (he ultimately chose to disarm and restrain her) and now he's in serious legal trouble. She ended up in the psychiatric ER. But hey, both of them are still alive.
My question is, how could a person possibly handle this crisis situation in a legal and ethical way, while both respecting her right to bodily autonomy and his own right to personal safety? Does he truly just have to forget about her immediate welfare, call the police, and walk away? And why were police so quick to pin blame exclusively on him, isn't it a crime to wield a knife in a menacing and threatening way (i.e. assault with a deadly weapon). Based on the information I have provided, are there any legal defenses that could keep this guy out of prison and his future intact? Thank you.

