If a Single person dies what happens to his mortgage?

The mortgage is still attached to the property. An heir can take over any interest in the property, as assigned by the probate court, but the heir will need to secure financing to cover the amount of money owed on the mortgage(s). If you're asking whether the mortgage goes away, no, the debt remains attached to the property until the debt is satisfied. Some banks offer "Credit Life" insurance which covers the mortgage, but it usually costs extra.