"subject to" buying options

[John Grover]

I am looking at potential liability of the following subject to deal.    Scenario...  seller went into strategic default on primary years ago.. he has been prolonging foreclosure via fraud claims against the bank.. all the while I am sure renting and paying nothing against the property.  He suggests he may have a good case however the bank also may move on him at any.  He is looking to cut a deal.. I believe in his mind something like this:   He transfers the property to me subject to mortgage with no expectation for me to pay his mortgage since it is being actively contested.  If he is successful in winning the case and getting the loan forgiven(days or years from now), I give him x percent of the proceeds on the future sale of the property.   If he is unsuccessful and the property moves to auction we are both out.   

I cannot think why a seller would want to do this?    Does anyone know if him moving the property to another entity (in any way) would give him potentially more leverage in obtaining a settlement or a modification from the bank?    He has indicated he has no concern on having a foreclosure on his credit.    Thoughts?

How could a deal be structured with someone that cares little about their credit yet wants a piece of action on the sale of their property?