2nd mortgage suing on foreclosed home

The Defendant’s home entered foreclosure and the Plaintiff bought (assumed) the second mortgage after default, but before foreclosue. According to Plaintiff’s council, before the foreclosure the original mortgage holder offered the Plaintiff a buyout to satisfy the second mortgage so the foreclosure could proceed (through e-mails). The Plaintiff accepted this offer of $6000, thereby releasing the Defendant of all ties to the property and financial responsibility. The Plaintiff didn’t hear from the original mortgage holder (according to Plaintiff’s council) after this agreement and the foreclosure proceeded and the original mortgage holder did not seek a Deficiency Judgment against the Defendant.
Rather than pursue the contract made with the original mortgage holder, the Plaintiff’s council has made it known to the Defendant’s wife that it wouldn’t be in the Plaintiff’s financial interest. A phrase was used that meant “it would cost more to pursue than can be gotten” according to Plaintiff’s council who explained it to the Defendant’s wife. The Defendant maintains the position that a contract was offered and accepted for a financial note (not property) and therefore falls under legally binding contract. The Plaintiff probably doesn’t hold the original second mortgage with raised seal so I think this could be argued as an asset rather than real property thus not falling under the requirements of paper signature in real estate law. Essentially, they own the contents of the box (asset), and can’t produce the box (original 2nd mortgage papers) Is this a wrong premise? I’m to provide the court with an Answer in a short period of time. I’m hoping someone can give me a precedent to cite. Thank you