See, I think this is where a pilot's ego can be his or her downfall. We all like to think that we have the power to smooth things over with a good PA or a steely look in the eyes. In reality, going back there to gang up on the passenger is not necessarily going to de-escalate a conflict and may in fact make it worse by causing the irate person to feel cornered. They might also be emboldened by the perceived support of their fellow passengers. Which is why I said I'd call security and let the professionals handle it, unless there was immediate physical danger to a crew member OR they really weren't going to get off the plane; however it appears that they reluctantly did agree to deplane.
Where, on an ERJ, are you going to stand next to a Flight attendant? The only thing you're going to do by going back there is block the very exit through which the booted passengers need to vacate the aircraft. You're just going to get in the way. The FA is just green and thus the tears....in this industry you have to able to shake this sort of thing off or you just won't last.
In the end, the passenger was completely justified in swearing at any airline official within earshot! That's what makes this different from most situations.....if the passenger is unjustifiably being an ass then yeah, maybe it justifies your intervention, but in this case they were clearly wronged and are 100% justified in being irate. Nothing you say or do is going to change that, and if they're getting off the plane anyway, it's a waste of time to go back there. Only the gate agent has the power to fix it via rebooking, compensation, meal vouchers, etc....the FA should just be telling them to direct their complaints to the agent.