If you sales contract states particular terms and conditions you may have to close no matter what or loose your escrow money.
Have your agent review all the circumstances with you.
Are you working with a Realtor? If so, that person should be advising you on what your next steps should be. I find it curious that the seller is not wanting to extend the closing date, is there more to this? Also, why did you switch banks because of the rates? I guess I have more questions for you than answers on this one. In this marketplace typically a seller will do what it takes to hang onto a strong buyer, waiting 10 days doesn't sound like that much of a concession. I am not sure about how NYS looks at time is of the essence clauses but in RI it usually means that the closing must happen on the date indicated on the agreement without extensions. I would recommend getting legal advice and/or at the very least let the seller know in writing that you cannot meet the December 4th date, otherwise your depoist held by the seller could be in jeopardy. Best of luck to you!