You might be able to argue that you have a fundamental constitutional privacy right to be free from an imminent threat of physical violence from others, and that the employer's termination creates a "chilling effect" on your rights, because it provides you with the untenable option of risking physical assault in exchange for losing your employment.
That's probably how I would draft a complaint against the employer, if I were representing you. Your case would be stronger had you actually contacted law enforcement at the time of the altercation and requested assistance.
You could also sue the bar for negligence in failing to act to protect you as a customer. But, that's a separate issue, and you would have to bring suit in CO.
Hope this helps.
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