Anyone -regardless of the legalities, or of any BS hockey conventions involved- who just stands around and watches such a beat-down needs to intervene, just by dint of being a human being.
I don't give a s*** what the officials' titles are, or what their bailiwicks' entail in a technical sense ... That was just wrong, and an embarrassment to the game. The zebras let the game down, any way you might choose to parse it.
Call me a "snowflake", but why is this BS acceptable on the ice, but not on the street? That makes zero sense. If that's the standard, well let's allow assault in golf, tennis, and curling. Poker, too. Why does hockey get a free pass?
Stupid beyond belief.