This conversation is just about Heiskanen though. Like FirstRow mentioned, Heatherington is NHL ready. Hamhuis was a luxury this year in that he stepped up big when Methot went down. Next season, the money just doesn't make sense IMO to sign Hamhuis as a guy to replace Methot in the Top 4 when he's injured. You have 2 young guys that could step in to that 3rd pair role. Just let them battle it out, but my guess would be based on Hitch's choices this season that Heatherington is your likely 3rd LD behind Lindell and Methot to start the season. Heiskanen goes to the AHL. It's disappointing that Bayreuther's developed has been a little slower. I didn't expect to him to set the AHL on fire, but it sees he's struggling still with the all around game. I'd feel more comfortable because of Methot's age and injury history, if Dallas had a third defender on a two-way contract who could potentially step in to a slot on the 3rd pair if Heatherington or Heiskanen were forced up the lineup because of several injuries. Nyberg and Vala will likely both be in the AHL or ECHL next season, but I doubt either is going to be an option in the NHL realistically in 18-19. I'd expect Dallas to sign another depth D or even re-sign Bodnarchuk.
Also, I'd be fine if Pateryn was signed to actually be Dallas' 7th D, but that's probably not going to happen. The best case scenario is someone desperate for a right shot D overpays him in free agency and Dallas walks away. If Pateryn is back on this roster, I don't have much confidence that he'll be sitting on the bench. That will likely be Honka, again. Hitch seems to like the R/L balance so there would be a chance Honka might have the opportunity to play over Heatherington and Heiskanen though.
My first choice at least consider what we know today:
Lindell-Klingberg
Methot-Johns
Heatherington-Honka
Heatherington and Honka were a pair for a year in junior, and they've been a pair in the AHL. It's a perfect situation where you have a guy in Heatherington who can support Honka's adventures up ice. In this scenario, I'd be happy to see a veteran, 7th defender added.