Wait, if OP themselves added a MIT license without getting a yes on it from their superior, they are already in hot water.

If it were me, I'd say that the license files should be _authored_ by someone in the company who has a say on such matters. Come on, if it's work for hire, the copyrights by default don't belong to you, so you don't go licensing it left and right, it's your employer's prerogative!

It doesn’t matter if the employee acted in good faith. The former employer can still lawyer up and create a problem. And there is a reasonable probability that no one with executive authority signed off on the code repository simply because of the way software development happens and the standards In industry.

To put it another way, the legality matters less than the relationship. A lawyer can communicate with the former employer in a way that mitigates potential problems. Or say it is unlikely to be a problem.

They could claim OP pushed for MIT specifically for this reason, to be able to take advantage of it after the employment is terminated.

Practically speaking, he can worry about it when that happens. If it becomes a problem, he can rewrite the whole thing. He wrote it in the first place.