Our biggest need, in my opinion, is patience. So much of our talent is under 24 years old, and very few of them have played even 200 NHL games yet. Makar, Kaut, Bowers, Timmins, etc. haven't even played 1 NHL game yet. And we still have 2 picks in the 2019 draft that look like they'll probably be lottery picks. Right now, it's hard to figure out what we're going to need next year, let alone trying to plan for the future.
As for Z, right now, I think we need him more than what we would likely get for him in a trade. The only other LHD who looks NHL ready right now is Graves, and he's not really the same kind of physical force that Zadorov is. My current long term guess is that in 2-3 years, Zadorov provides the physical defense to allow Makar to do his thing, and Girard plays with Timmins/Meloche. Obviously, a few things need to go right for that to happen and could change in the near future, but that's my working model.