Checking on Project Helius website, you could see a VR-demo option. Download that and played (you will be directed to vrporn.com to download), it is the exact same content as the uploaded ones previously. Also check their Patron tier description, it also specifies a "full version" of the game if you pledge enough. Also on the vrporn.com, it also specifies there is a "premium" version of the game. At last, the NON-VR version does not give you the option to play story mode.Which links do you mean? All of the non-VR links in the OP still work. But you are right that only one link of the VR build is still working. But I'm sure that changes if and when someone shares the 1.28 VR build.
I was not aware that there was such a thing as a demo for this game. Or even a full version. As far as I know, every single build we've seen thus far has been an alpha or beta build, since the game is still in development.