For Dallas to move on from Heiskanen I think you'd be looking at a guy like McDavd being the return. Dallas would obviously be adding, but to go lateral with Heiskanen doesn't really make sense IMO.
Tempting as a neutral fan though, I'm thinking Dallas could line up something like this next year:
Hintz/ Cogliano/ Janmark - Seguin - Radulov
Benn - Hayes/ Duchene/ comparable player signed in free agency - Boeser (after this trade)
Something like this as their top 6 next season would be really fun to watch I think. But the reality of the situation is Heiskanen's stock keeps rising and he is already a top 4 D at a young, young age. His ceiling is franchise defender and those guys only come along so often.