Seems like its only going to be VR. Thats sad. I love halflife games but I am not going to shell out hundreds of dollars for a VR headset to just play that game.
I see it the other way around -- lots of people have shelled out for a VR headset and need quality content. (valve's lab was good but just a teaser)
If they developped it with VR in mind from the start there is no way to adapt it into a non immersive version.