Penny ran on the Independence Party ticket for Governor in 2002 against Pawlenty and DFLer Roger Moe. I doubt that the Democrats would take him back unless they were in a real bind to find a decent candidate, and I doubt that's going to be the case.
I meant he would run as an Independent. I don't think Penny would even try to go back to the DFL party. From watching him over the years, I think he is too moderate.
He was pretty conservative in the House and worked well with John Kasich. Maybe he would run as a Republican.