Re-entering with an expired FM3

Friends of ours left Mexico City due to illness. The immigration officials told them to cancel their FM3 at the Consulate in their area. They went to the Consulate in the states and were told the FM3 should have been canceled in Mexico.
The FM3 has now expired. They are planning to return to Mexico to take care of this. Does anyone know what will happen when they arrive at the airport in Mexico (with immigration) since their documents are expired. Also...the steps required to clear this up.
They are not interested in renewing the FM3 only traveling as a tourist.

Very simple. It has expired. I'd carry the old ones if the topic even comes up to show proof of expiration but use the tourist permit process that they do on the plane. The FM3s have expired so now they can just use the tourist permits when they come.

From personal experience, the actual FM3 document is the property of the Mexican Government and must be returned if expired. Get caught with an old expired FM3 and one may face a hefty fine. Using an FMM as an entry and exit document after a FM3 has expired shouldn't be a problem.

YMMV!!!!!!!!!!!!!!!!!!!!!