First, everything is negotiable. Per law, your lease may no longer be valid if the mortgage was in place BEFORE you signed your rental agreement. More to that on the website below.
In regards to "cash for keys" the amount you can get paid for voluntarily moving out is definitely negotiable, too. Let's say you find another place to live and they are asking for a $1,000 deposit and you need a moving truck that's going to cost you $100. Get it in writing and present your case to the PAS rep - more likely than not they will give you the $1,100 in return for you leaving the house in an orderly manner and leaving no trash behind etc.