An app can be used without any error by purchasing "No Watermark" add-on from the project dashboard during your PRO subscription period.
This will cost 699 USD per project.
The addon will allow your packaged app to run without issue/watermark after unsubscribe, but you will still not able to log back into your InstaVR Dashboard to make changes/repackage your InstaVR projects after you unsubscribe.
InstaVR - Make VR apps in minutes! Grow Your Business Using Virtual Reality