Does my friend need to change his Non B visa after marrying a Thai spouse?

Only possible benefit to change to spouse extension atm is if he suddenly loses his job, Spouse extension will allow him to stay without working/between jobs.Empioyment isn't mandatory for thai spouse/ext, just proof of funds.

But same can be said if wife suddenly divorce, He can stay on b visa/extension.

Continue as normal.

Nothing will change if he doesn't want to switch the reason for his extension. In the future, if he decides to change, all he has to do is make sure his bank account has at least 400,000 baht around October and stays at that level until he applies for his extension, and instead of applying for the extension based on employment, he would apply based on being married to a Thai. It won't affect his work or work permit at all. In fact if he's still working at that time, he can use proof of his salary over 40,000 baht per month and won't even need the bank balance.