In two weeks I'm traveling SFO-MEX-GDL return is GDL-LAX-SFO

I'm looking to actually STAY in MEX (Mexico City) and drive to Guadalajara with family. That said, I do not want to have the return portion of my trip canceled for a no Show.

Mexicana is the ticketing airline and they are not helping (or unable to help) other than saying I may be able to be reticketed on the day of travel.

Travel agent is being difficult.

any thoughts or experience here?