Both are technically invalid the day he finishes work.
The non-b is only valid with a WP. So officially he's meant to leave when the WP is finished or before that if his contract ends before. Remember taxes are due until he 'officially' finishes work.
Yes both need to be cancelled and if its your/his business the company needs to be closed and the companies bank accounts too. Tax receipts up until the end as well.
If he plans to come back with a proper visa as you say he is then yes it all needs to be cancelled or he is likely to have problems.
If he was leaving and never coming back he could just walk. But the visa needs to be cancelled even if he was coming back on a border bounce.
In short yes he needs to cancel everything officially the day he finishes work officially and leave Thailand.
You can get a 7 days get out of Thailnd 'extension' you apply and get rejected and get given 7 days.
I wish I could remember the order it all needs to be done.
Signing up for a course, paying the money for the course and visa, worrying if you will be tested and refused entry, finding the program gets cancelled sounds like more hassle to me.
It hasn't happened yet, it likely won't until the government changes back.
It's all politics between 2 sides constantly trolling each other.
If it changes back then you either apply for a 60 day tourist visa before you come or get a 30 day visa exempt on arrival and get a 30 day extension at the local immigration office near the end if the initial 30 days.