I see two scenarios here.
1. Its obvious that Johansson quit playing because of Cassidy. That ire was not directed past Cassidy to the team because McPhee kept him on the payroll and Johansson wanted to stay with the team. Just away from Cassidy. With Cassidy gone, Johansson can return to the ice and the Caps certainly can use him.
2. This could be a long term return to the Capitals. Hanlon is a promoted assistant coach. That leaves room for another assistant coach. it could well be Johansson. He could step straight into that job rather than play. He could play and coach after he is done. He could do both starting the first of the year.