So I am not advocating for Voynov, let's be clear. But for the sake of discussion, at what point does a person get a second chance, even from something as egregious as what Voynov did?
Evander Kane chocked a girl in a Buffalo bar
Patrick Kane was accused of raping a girl and he punched a taxi driver
Danny Heatley killed his best friend racing a car
Varlamov's issue with his girlfriend (this one I don't know all of the details)
NHL Players and the Law
All of these "where is the line" kind of questions are seeking answers that don't exist.
Where the line is will change from person to person and obviously from team to team when a potential player is involved. There is no objective answer and never will be.
In my opinion, Voynov's actions obviously not being accidental in any way combined with them being absolutely proven to have happened is way past the line.
Accusations are troubling but we don't punish people solely based on accusations in the legal system and I don't think we should in the court of public opinion either. Evander Kane's issue didn't go much beyond accusations last I heard though I admittedly haven't followed it much since. Patrick Kane's rape accusation didn't go past an accusation ultimately either if I recall correctly.
Patrick Kane hitting the cabby was beyond stupid and reflects very, very poorly on him. Having said that, he wasn't preying on someone who he is in a position of trust with and last I heard he didn't come near doing the same damage that Voynov did to his wife. I'm not saying what Kane did is ok, but I think there's a pretty clear and logical argument that was Voynov did is way, way worse.
Heatley's thing, obviously he was driving like an idiot but one can at least argue that he didn't mean to hurt or kill anyone. Yes, hurting/killing someone is a foreseeable potential outcome of driving the way he was, but plenty of people drive like idiots without hurting anyone. Nobody beats their wife without hurting anyone. Nobody beats their wife by accident.
There are no hard and fast rules, everyone will decide for themselves and compare the situations in question.