If your scenery is not purchased, buildings will disappear after about 5 minutes, that's exactly how the Trial works. You should also see a message in red at the top of the scenery stating the Trial has ended, but it might not appear 100% syncronized with the actual buildings disappearance, it might shows a short while after that.
If you are having problems running the software, buildings will not disappear after 5 minutes, they will just not appear from the start, but this will also mean there will be no "Addon Manager" and no "Couatl powered products" menus under the Addons menu, because if the software is not running, its menus will not appear.