One can hope! Your security deposit is the personal obligation of your landlord, not the new owner. The only exception would be if your landlord gave the new owner the deposit amount and notified you that the new owner was, in the future, going to be responsible for your security deposit. I assume that didn't happen here. As such, the new owner is not responsible for the security deposit. You can sue your landlord in small claims court for the return of the money if you serve him with a complaint. He will be entitled to an offset for any rent he applied the security deposit to.
virtually no chance of getting it from a foreclosed landlord. you have a right to it though and perhaps a shot at penalties
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As stated above, your old landlord is responsible for returning your deposit, but his inability to pay the mortgage does not bode well for you getting it back.
But you are still liable for December's rent. It was due on the first, and you did not pay it. Your landlord's directive not to pay it does not mean you do not still owe it. It just means that he could not turn around and give you a three-day notice when you did not pay it on the first.