Since version 1607 of Win 10 you can swap motherboards and still remain activated, meaning no new licence needed. Admittedly, if he did swap motherboard between now and then he would have to contact Microsoft and see if they reactivate it for him, but after 1607 you can swap every part of PC out without worrying about reactivation - there may be a limit to how much can be swapped but I have yet to hear of anyone deactivating since. I am sure I will, sitting on these forums.