Hi Mark, nice to see you here! I came on here wondering the same thing, regarding the same issue for a board I am affiliated with. Not having set up a terms of service from the start, the owner of the board is now concerned that he has created a sticky situation for himself which a TOS would not necessarily fix at this juncture.
So for anyone who has run into this situation, the question remains: what are the legal considerations and options when TOS had not existed formally prior to any issues arising?