Are you saying that they will no longer be accessible from the warehouse online but would be from me if I download the models now?
They should still be able to access anything that is in the 3D warehouse after Jan 31st and they are using supported version (like the free online version). So far, the only place that I have seen the message is when I downloaded something from the 3D warehouse and requested it be downloaded into 2017 format. I just tried uploading a file in 2017 format to 3D warehouse and it did not give me any sort of warning about not being supported. So this may, for now anyway, just apply to downloading from 3D Warehouse into an unsupported version but I would not count on it.
UPDATE: I just tried to download something from the 3D warehouse so that I could capture the warning message and now it no longer shows the option to download into 2017 or 2018 and the warning I saw before is gone. It was there this morning right before I created this thread so they removed the ability to download into 2017 and 2018 formats in the last hour or so.
--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.