The more time that passes, then the greater the chance that any dismissal
(that's what we're really talking about here)
will look like an "Unfair Dismissal".
I hope that by now, you have taken Rod's advice, and joined your union.
You are forunate indeed that nothing has come of it so far.
I am a broad minded, tolerant, and thick skinned, employer.
But to even threaten violence against a colleague,
I would have had you out the door instantly.