There's an issue with getting 'on save dialog cancel' to trigger in construct 2. It just won't do any actions assigned to it. I've attached a simple .capx to illustrate the issue using nwjs v0.50.0 and C2 r279.
https://drive.google.com/file/d/1cWxau4ZLdKxaOBMbZaEZtxZO9JRbJHEB/view?usp=sharing