If they crack down on reselling parts someone will just create a new platform doing that. What might be lost is some of the custom builds stuff and "automatically find parts" functionality. At last for some time.
Through they might put up a bit more quality assurance, i.e. follow complains about non-official LEGO parts being sold and similar. It also prevents the platforms from starting to sell non-Lego blocks and figures.
Through we probably can be sure that militaria LEGO builds are not unlikely to disappear.
My concern would be that Lego will make BrickLink the "approved" community and resale site and make it harder for alternatives to exist.
I hope I'm wrong, but I cant help but think that because the resale/collector value of Lego increases it would make sense for Lego to try and control that market.
There already is https://brickowl.com