Is Mike McCarthy possibly the Saints next head coach if Dallas lets him walk?

No, I don't think he is.

I think Dallas will want to keep him, but he may want to go elsewhere. Away form Jerry. With an expiring contract, it's not just Dallas that has the final say.

I like crazy theories, so I say Jets if he leaves Dallas.
He worked in New Orleans in the past, but the team will take 3-4 years to rebuild and I doubt he wants thAT HEADACHE.