Scenery doesn't disappear like that, the only possible explanation is that you download the update instead of the full installer, and that one didn't completed
something was wrong in your scenery.cfg, the installer told you, you haven't noticed it, so the installation aborted without copying any files.
You simply haven't installed them in the first place. From what you are writing here:
The other day I purchased LAX and JFK together and received my Serial Keys via email as normal
You don't say anything if you installed them or not. Just purchasing will not result in the scenery loading, you can purchase without problems even if the scenery is not installed, but you have to install it to *see* it.
Just the sceneries, and they'll work.