By reading the continuation of the linked post above, you would have found:
This means for a model uploaded with SketchUp 2014, skp files for the last 3 versions (2017, 2018, 2019) and the original version (2014) and a COLLADA version should be available. Your SketchUp 2016 should be able to download and import all models from 3D Warehouse if they were originally uploaded with SketchUp 2016 or before. This is because the desktop client contains importers for (usually) all older formats, but no newer formats.
By contrast, the converters on the server (to convert newer files to every possible older file format) will not be maintained for ever because that costs effort for no gain.
You paid for a perpetual license of SketchUp 2016 which was supported until the next major release. That means you are still licensed to use offline functionality as long as you want (which should work forever in an isolated environment), but since support is over one should expect that dependencies to the external world (web services) will break as the world moves on.
Software does not work like a house that you can buy once for eternal use. Therefore there exist very affordable license upgrades (compared to buying a full license) that you should not miss out for too long.
[Personal opinion, since I am not affiliated with SketchUp]
- I do however agree that it would be less detrimental if SketchUp discontinued intercompatibility to competitor’s formats rather than their own.
- Launok has also shown the benefits of an extensible file format: The same Collada files still can be read after years in new and old SketchUp versions (at worst only a subset of features within the file can be imported, but most of the time the software does not completely refuse the import).