Well, I dunno how to feel about Matheson. He's good going forward but an absolute nightmare in his own zone...
Matheson will continue to improve defensively as he matures. And importantly, he should not be paired with Letang.
Pettersson will continue to improve both defensive and "offensively". I put that in quotes because it's not direct offense or running a PP, but rather in transition, joining the rush and pinching in.
Dumo is still the guy who has to go, as Pettersson has really been playing some great hockey the last couple of weeks of the season and in the playoffs. We have to throw him into the deep end next season and let him sink or swim (aka pair him with Letang, and Matheson with Marino).