Second, and a little harder... what to do with the deposits that do not get withdrawn before the site shutdown:

In a perfect world I'd like to hold the deposits 6-12 months so that people could continue to make claims and withdraw their forgotten coins.  I do not believe I am going to be allowed that luxury.  Thus, despite the risks, I suspect I am going to have to process refunds back to the address of a user's last successful withdrawal.  I know this is not ideal.  Some portion of the withdrawals are going to go to addresses that are no longer used, or are on sites no longer in service... Can anyone think of a better alternative?