I believe someone who is not taking closer looks of what is happening would be very pissed when he founds out he missed some cut-off date, which he was never informed ever existed. It's very reasonable to assume there are lot of people trusting the site and never bother to check their BTC, treating the site as some kind of online wallet service. Of course you can not take care of their money forever, but one month cut-off date looks very, very short to me. If you ever decide to go this route, and inevitable face some very pissed off people in the future, make that cut-off date much longer, at least a few months, to maximize the chances one will eventually check what's happening. Also, i think it's very reasonable to change the front page with clear notification that end-of-service is closing. Notification in the chat area is not enough.
May I suggest other course of action that may solve your problems: Find a trustable escrow service, who is willing to deal with this situation, and send all cut-off money to them. This way you are relieved of all your obligations to the government because you are no longer in control of the funds, and those coins would be eventually retrievable from the escrow when some day owners remember they had some funds on JD.
I agree to this, what if someone went on holiday for a month or so? Or what if someone invested and just waited for a fee months before checking up on it because he doesn't immediatly need his bitcoins and he does not feel the need to check back often?