McDonagh is a tough one. Rebuilds don't always take as along as some think. Toronto set out on that path after the start of the 15/16 season when they parted with Kessel and Phaneuf, and frankly, were in a similar spot as the Rangers are right now.
12/13: Leafs made the playoffs = 16/17 Rangers made the playoffs
13/14: Leafs struggled = 17/18 Rangers struggle
2014: Draft, Leafs got #8 OA pick (Nylander) and got the #22 OA pick (Kapanen) via trade = 2017 NHL Draft Rangers got #7 OA pick (Andersson) via trade and #21 OA pick (Chytl)
This is about where the Rangers are right now.
2015: Draft, Leafs got #4 OA pick (Marner) and an extra 1st (due to trade deadline deals the prior year), which they traded down to the 2nd (Dermott).
2016: Total tank job and got Matthews.
2017: Back in the playoffs only 2 years after parting with Kessel and Phaneuf.
The Leafs had some good, young (ish) pieces in place already (Reilly, Gardiner, Kadri, JVR, Bozak) so that when they rebuilt, it didn't take long. IMO, that's where the Rangers are. Rangers have a lot of good, young (ish) pieces still in place in NY (Miller, Kreider, Hayes, McD, Zib, Buch, Skjei) and with some shrewd moves, could be back in contention in as little as 1-2 years. Of course, it all depends on what spot you get in the draft, but I think the bones are there for a quick turn around if done right (unfortunately, as a Canes fan). Guys like Nash, Zucc, Grabner, Staal etc.. are easy moves. I'd be hesitant to move guys like McD unless the return is spectacular. I would hold on to most of the other young guys I mentioned unless it's a move for a young player that plays a different position (Offense for defense move for example).