By filing the OSHA complaint you have immunized yourself from being terminated for making the complaint. Legally, insubordination towards a supervisor will permit a termination, regardless of the OSHA immunity. However, in this circumstance, I don't see how the employer would be able to separate your conduct from the safety issue, itself. In other words, if you are terminated, your response is to file a retaliation complaint. The employer would have to prove that you made the statement, that it was entirely independent of the safety complaint, and that the employer's termination was equally independent.
That would be pretty difficult to do, and the employer's risk of losing the action is high.
So, the answer is "yes," the employer can terminate you, assuming all of the above-described risks -- so I will be amazed if your termination actually occurs.
Note: This doesn't give you a blank check to disparage your supervisor. The further away that your conduct occurs from the complaint and safety issue, the greater your risk of termination.
Hope this helps.
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