Leon hasn't appeared in "The Conners" yet, and they haven't really mentioned him by name.

I'm assuming he and Scott left Lanford after The Lunch Box went under (although the writers don't come right out and tell us, I'm assuming the family restaurant was a casualty of The Great Recession).

However, in "The Conners," Jackie and Becky buy back The Lunch Box from its previous owners and repurpose it as a comfort food diner. So if Leon was going to resurface, I'd assume his old business is one of the first places Leon would head to.