My mother died in August 2010. I have been paying the mortgage, though not on the loan. (I am on deed) What happens if I let the property foreclose.

You haven't provided enough information for me to understand clearly what the circumstances are.  If your name is on the deed but that you are not obligated on the loan, it appears to me that you allowed your real estate to be pledged as collateral for your mother's loan.  If you allow a foreclosure, you will quite obviously lose whatever interest you have in the realty.  If your name does not appear on the Note (the promise to repay the loan), then the lender cannot sue you for any deficiency.  You should confirm that your name is not on the Note before you allow a default to occur.  You did not ask about the car but, it appears to be that if the car is still in your mother's name, at some point you will need to get it into your name if you claim to be the beneficiary of the vehicle as a result of her death.  If that is the only thing remaining that needs attention, your attorney could possibly prevail on the license commissioner to accept a copy of the will and an affidavit in lieu of probate.  If not, I think you will eventually have to probate the estate in order to clear title to the car.  You should confer with your attorney about both questions.