The problem with moving Polanco over to SS is then we are returned to a very poor defense up the middle. Polanco has seemed to regain his skills as a decent hitter but he is still a subpar fielder--especially bad at SS and extremely bad in the late innings of tight games. His late inning flubs have cost the Twins plenty including the loss to the Astros in Game 1 of last year. Moving Sano over to 3rd is even a less attractive idea. He moves around like a sofa without casters. I can accept that at 1st base (somewhat), but not at 3rd. I know there has been a lot of carping about Simmons at SS, but none from me. I knew he was a bad hitter--maybe not as bad as he has been, but I never advocated getting him for his bat. I wanted his glove. (Think Mark Belanger. One of the reasons the bygone Orioles were so good was their defense was stellar both on the infield and in the outfield.)
Personally, I want to keep Sano. If he can get his head screwed on straight, he can be a devastating asset. If he can't, we can eat his 12 million dollars as Bean5302 has mentioned, it won't break the bank.