Regardless of the result of the company enquiry, in the UK at least you would have the option of reporting the captain to the police for common assault. It would appear from your reporting of the incident that the other crew member who came to your aid may be caled on as a reliable witness.
Wouldn't help your position in regard to the incident, but should a 'stitch up' take place over the enquiry, which you appear to be worried will be the case, it may well provide some element of justice against your crazy colleague.
I have colleagues in dispatch who have been assaulted by captains of overseas aircarft (I'm sure most crews would like to assault their dispatcher from time to time), but this activity has always been frowned on severely and reported as appropriate, with the company refusing to provide any further services to that aircraft.