I can't see exposing Greenway if he continues to play as well as he has. What's the point of trading Greenway for a later 1st rounder, or Amirov, or Robertson, when Greenway is precisely what you want a prospect to turn into, a NHL player, and potentially an impact NHL player?
Maybe, in a perfect world you trade a resurgent Dumba and Greenway for Nylander with maybe a small +, depending on how all the principals involved in the deal are playing at the time. Greenway would have to be playing at a .7 PPG pace, Dumba at a .5 PPG, etc.. I'm still not in love with Nylander, and am not sure if his game will survive if he is moved to Center.
Overall, I am very lukewarm on the idea of moving Greenway. He is not an elite first liner or anything, and never will be, but he is the epitome of a quality young support player that any successful team needs if he continues to play as well as he has shown so far this season. I don't see trading him for a maybe.