If 100% of the code was written inside the company then they own the copyright and can do whatever they want with it
It depends on his contract with the company. It's not "their code" automatically.
Thank you my good man for correcting this young fellow with such a high ID number. I'm not english at all and was very curious at your suggestion, but I knew that the internet would settle your disagreement once and for all, for it seems that "In American English go is sometimes followed directly by a bare infinitive" (source).
No, I'm not drunk.
If I'd known computer science was going to be like this, I'd never have given up being a rock 'n' roll star. -- G. Hirst