Yes! It is possible for the forums to be shut down, and that could be, because of some reasons by the people in charge of the controlling the system, especially when some illegal activities are detected, like malwares, so it can be shut down to enable them tackle the issues, and provides security for users. But due to the decentralized nature of Bitcoin, there will always be a way out, as other means can still be developed so it will still be operated.
It can only happen for awhile but it will not take forever because Bitcoin, or it trading has been adopted globally, so it usage can never be eliminated because there will always be a way to restore the operation.