Maybe it's a problem with some nw.js process not responding. Could you look at the task manager? In that case ending the nw.js process might fix it. I'm going to investigate, I've started and closed the game many times to confirm that it starts up fine and I've never had a problem.
There were about 5 "XXXXXXX.tmp" processes running in the background that after I killed them the game was able to launch.
I tried an ESC close, and the game relaunched fine. I ALT+F4d close, and the game *still* relaunched fine. I don't know why the temporary processes stuck around. Possibly because I first launched the game from within the ZIP?