What should a foreigner do after being fired while holding a work permit in Thailand?

Hello, I have a question for a friend who is not on facebook. He lives and has a work permit on Samui with the same company for 5 years now. He has been suddenly fired/let go. The boss has paid for his work permit already, which expires in December.

What should he do at this point? How long does he have to stay in the country? When I searched this group, I found that he must go and cancel it at immigration himself. Any further advice?

Thank you