Would DAL make a great trade partner for Nylander?
Stars' fan here. Respectfully, no. We'd love to have Nylander but we have no one who fits the bill as to what you need on defense. The quality defenders we do have aren't for sale (Klingberg, Heiskanen, Lindell) and the rest (Methot, Johns, Honka) aren't enough to be a centerpiece in a deal for Nylander.
Additionally, from everything I can tell, Dubas is simply not going to move Nylander. We had a similar situation with Benn when he signed his bridge contract. He missed a few games and they eventually settled in the middle (5 years, $5.25M per). Nylander has a bit of a better track record than Benn did at that point, but his game isn't quite as dynamic as Benn's and he may not have the ridiculous ceiling that Benn did either (not to disparage Nylander or anything at all, he's an excellent young forward).
I wouldn't worry about the contract or long-term relationship - it's just business. If he's not signed a month from now, then maybe worry, but I would be shocked if that's the case.