You are always thinking, Robin

Typically before a property listing has expired, the listing agent will have already spoken with the sellers and had them sign a new listing agreement and they will relist the property.
While that is the way it happens most of the time, it does not always happen. There are many realtors that will search consistantly to contact sellers the day that listing expires to attempt to sway the seller to list with them.
Most expired listings relist their property. There are however those properties that may have been listed because the seller simply could not afford to remain in the home and it may expire during the process of foreclosure. You could attempt to follow up on those and try to purchase them from the bank that carried the loan.