What should my friend do about his non-B visa after his work permit cancellation in Thailand?

Is he on a non-B visa? or is he on a work extension? That makes all the difference on what he needs to do. If he's on a visa, then he doesn't need to do anything and can stay until the end of his existing stamp. If he's on an extension (the stamp in his passport says "extension of stay") then he must go to the immigration office that issued the extension with documentation that his work ended and cancel his extension. If he goes past the date on the documentation, he will pay 500 baht per day fine for failing to cancel on time.

If the work permit is cancelled then the extension of stay must be cancelled the same day. On the slim chance they are on an actual visa rather than an extension of stay (look in passport) they can stay until the visa expires

When the WP is cancelled the B need to be too. Employer cancels WP then employee must go to Immigration and cancel B. The B is tied to the WP and is invalid when WP cancelled. Normally have 7 days to leave Thailand ie can do visa run. He can go to Immigration Monday.