Hi,
It'll behave like mentioned in the B option. As there will be no available license (it'll be already in use), the other user will get warning message and if he needs to work with our plug-in(s), he have to wait until the license will be "returned" to the licensing server.
The license handling process is fully automatic - the license is sent when needed and released to the "free & available" status when not in use - that happens shortly after closing the 3ds Max (within seconds) / scene with Forest objects (within minutes).
Best regards,