I may not have been considered a real cofounder but I was there at the first brainstorming and had all of the technical ideas. I had a lot more ideas since and am building another team to start the business again. Forced to bootstrap and then move to another city because all the investors here have invested in my original company!
If they fired him, that often renders agreements unenforceable, or at least difficult to enforce outside of rare circumstances. Even in states which otherwise recognize noncompetes, courts tend to be hostile towards companies that try to enforce them against employees where the company themselves terminated the relationship (though not all states are equally hostile).
For example, here is some pretty direct language from the Montana Supreme Court [1]:
We agree that an employer normally lacks a legitimate business interest in a covenant when it chooses to end the employment relationship. [...] An employer needs no covenant to protect its business in these circumstances as the employer sits in the best position to protect itself simply by maintaining the employment relationship.
I've spoken to their lawyer and also got a second opinion. There wasn't a non-compete and both said I could start a similar company as long as I don't use any source code or other work created previously.
