Prevent app from closing

You can kind of do it. I did it accidentally last week and the only thing I could do was restarting the watch because I returned true onBack and didn't do anything. But I think it might be possible on some devices to get out of the app still with key shortcuts.

If you return false from onBack, it will take the default actions on the main view, which is closing the app.

I have apps where depending on it's state (for example if there is a recording in progress), onBack returns true, while other times I return false and the app terminates.

Great, thanks. I will check it out. 
Is this the only method/ creative way you are aware of?

One thing you want is a similar UI to other apps, but something you could do is always return true with onBack, then you use the menu key (onMenu) to offer a "Exit app" selection.

I think if you make it too hard, the user will just power cycle the watch to kill the app.