re: If a piece of property is going to the sheriffs sale

No. You don't have to assume the debtor's note. After the sheriff's sale you get the property free and clear of all encumbrances. If the mortgage holder wants to protect its interest, they can bid to buy the property for the amount of the mortgage. If someone bids higher, the lien holder gets paid off the top. If you are interested in assuming the note, you would have to make a deal with the debtor and creditor before the sheriff's sale.