You can keep using all our premium products on the licensed domains even after the subscription period ends. However, you will not have access to product updates, the premium support forum or documentation, unless you renew your subscription. Regarding MJ Pro specifically, you will lose also access to the remote online device database. Your mobile website will keep working, though, since Mobile Joomla! Pro will automatically switch to use the included backup offline device detection. But you will have to do manual updates to get new device support updates.
The 200,000 monthly remote device detection limitation clause is mainly a safeguard for situations where a high-volume site would cause bandwidth issues. However, we've been able to optimize the device detection functionality so much that we've never needed to look into that. In any case, we won't ever cut off anyone's website, but instead negotiate a mutual solution.
Hope this helps,
Miikka