I am going to say...
Pardon me as your question was pending for 3 hours in Post.... I will attempt to reply.
As your friend is on the INITIAL 90 DAYS of the Non B Visa and it HAS NOT been extended...IT WILL EXPIRE on departure or not later than February 15th.
Then your friend can stay no longer than February 15th.
Make sure his work permit has been cancelled. It's his responsibility to cancel it.
Please check back with us tomorrow as it's Wednesday 10pm nightime in Thailand and added Moderators are available during the day.
But I believe that I am correct.
Hopefully... possibly, others ...
@Stuart ********
,
@Robert ******
...knowledgeable, can add their replies to you.