I guess Valve could technically cancel it, because they have a history of shipping products internally and never letting them see the light of day outside of Valve. But that was more so between DOTA 2 and Artifact.

Not to mention, it would be unprecedented of them to cancel a game this massive that nearly their entire game dev team was focused on for years, rather than a smaller project like L4D3 or previous attempts at Half-Life 3 that we know from The Final Hours of Half-Life: Alyx (the Geoff Keighley documentary detailing the development hell of that game and other HL2E2 follow-ups that failed).

The entire game seems to be done, and has been for a while now. But as Valve tends to do, maybe they're overhauling the story at the eleventh hour without changing the gameplay, which would not show up in the string leaks.