Buyer went missing, what are my options?

[Patrick Philip]

I got a house under contract over a month ago, set to close on 9/19/18 (two days from now). It passed the inspection period fine. Their appraisal came back fine. Now I hear that they haven't signed a disclosure agreement with their bank. Neither their agent or the bank has been able to get a hold of them for several days. If they never respond and go missing, the bank will not lend without the signed disclosure.

I don't see how they have the right to back out for no reason. Can I legally force them to continue the transaction?