I also worry about that point.
But so far, there were no VR games on GOG, so I'm afraid we're stucked.
That's not completely true, e.g. "The Solus Project" (GOG version) runs nicely on my WMR since the latest update. The only issue is that motion is done via the trackpads and not the thumbsticks. But that's an issue with many games designed for the Vive, also on Steam.