Agreed, it is a two year timeframe for inactivity.
See Item #8 for answer to point/account expiration.
Good question. Maybe the 'powers' can weigh in. There's nothing in the T&C that I saw to address re-instatement. My guess would be probably not because all the changes in their programs I have encountered regarding points are to get them to expire. Expiration = less liability. The timeshare program as re-done has points expiring after two years whether you use them or not.....no extension even with activity. Use them or lose them.
Under the Terms and Conditions of the Program, if there is no point activity over a two (2) year period, Marriott reserves the right to expire any points at that time. However, I doubt they would do it but one never knows.....
If you have a Marriott Visa and buy something...the points addition from purchases does keep the activity calendar window moving.