That he was traded is not surprising, the return is not surprising, but the trade partner certainly is.
Rig was the logical candidate to go with the logjam on D about to get even worse with Schultz returning. I still wouldn't be surprised to see Maatta go, but only if in that or a parallel deal a replacement, a la Muzzin or Martinez, come back the other way. Otherwise you run:
Dumoulin Letang
Maatta Schultz
Pettersson JMFJ
Riikola Ruhwedel
and call it a playoff roster. I'd be comfortable with moving Maatta even if the replacement D is only a rental, given that both Riikola and Pettersson should be everyday starters next season. As is though they are too green to rely on both for the playoffs, especially if one has to get forced into the top 4.