In employment law, there isn't a lot that you can do in terms of protecting your job, based on an employer's decision to assault you. You can certainly sue him for assault, but that doesn't protect your job.
If the employer here chooses to try and say that you quit, you can also fight that and obtain unemployment. The fact that you left the room after being assaulted is NOT going to be considered a resignation by any state. So, if he removes you from the job, you can file for unemployment.
But nothing about these facts creates any sort of wrongful termination claim. That is restricted to two very narrow situations. 1. If you have a contract of employment stating that you can only be terminated for cause, you can sue for breach of that contract. 2. If you are terminated here and can allege that it is based on your race, religion, gender, age, disability or recent medical leave usage.
Without a contract, your employment is "at will" and you can legally be terminated at any time, with or without cause.
So, the facts you've presented here only really give you protection from losing unemployment (by his alleging that you quit) and a potential personal injury lawsuit (in small claims) for assault.