A landlord CANNOT unilaterally terminate a lease. He can sue to evict you if you violate the lease, but first he must issue you a notice to correct the violation, and if you do, you cannot be evicted. But you haven't done anything wrong. To end your lease early, which is what he obviously wants, BOTH sides MUST agree on the terms of the early termination.
You could agree to be out by the end of November if you want, but I would demand at LEAST two months rent refunded to you for your inconvenience. That means not only do you not pay for December, you get October and November refunded, PLUS your full security deposit. Any agreement you make with him, GET IT IN WRITING (and I suggest having a lawyer write it and approve it before you sign it).
If he won't budge and insists on getting what he wants, respond to his letter with your own, by certified mail with proof of delivery, informing him that he, or the new owner, MUST honor the lease to its conclusion, and that you will be staying until the lease expires. The only thing he can do then is sue to have you removed, and he will be shocked when a judge tells him he can't have you removed.