I don't know about your state but here you cannot be fired for going to school as long as it does not interfere with your work. It would be like your job telling you how you can spend your free time.

Here if they were to fire you then you could get unemployment benefits. If you can get by on unemployment while you attend school then I'd just continue what you've been doing. All I can say is document EVERYTHING. That way if they fire you you can prove it's retaliation for not quitting school. That should entitle you to unemployment. Good luck.