Again, not sure if it’s a reliable source, but 2 a Day at Wordpress had this plot summary:
“After winning back to back Piston Cup’s (seen in glorious flashbacks of course), McQueen retires with Sally and the little subcompacts back in Radiator Springs where he teaches up and comng Piston Cupers … his kid-CARS don’t believe dad could once be a great racer so McQueen joins the great race around the world for one last thrill.”
I can’t see this as being viable.