The question Valve must be very tired of still hearing 12 years after the launch of Half-Life 2 is, when will Half-Life 3 be released? It's likely never going to happen, or at least not until Gabe Newell decides it is going to happen. And if it does happen, Valve is going to need some fresh writing talent as it now has no primary writers with Half-Life experience left.
Writer Chet Faliszek, who worked on Half-Life 2: Episode One and Episode Two, as well as Portal, Portal 2, the Left 4 Dead games, Counter-Strike: Global Offensive, and Dota 2, has left Valve after 12 years of service.
Faliszek gave no sign the departure is linked to his work at Valve or the games currently being developed and supported there. Talking to GamesIndustry.biz he said, "I worked there 12 years, shipped a bunch of great games and some amazing hardware and wanted to change things up. There's no news on what's next etc, I will let you know when that happens."
So for now, we don't know what Faliszek is going to do post-Valve, but his last role at Valve was developer relations liaison for virtual reality linked to the Vive VR platform. His future could be in VR, video game writing, or a combination of the two. With 12 years at Valve on his resume, he won't be short of offers and can take his time choosing what comes next.
Faliszek's decision to leave Valve is significant because he was the last of the Half-Life writers at the company. Eric Wolpaw left in February, and Marc Laidlaw left in January 2016. If Half-Life 3 is going to happen, then new writing talent will be required. I'm sure Valve won't have any trouble filling that position if indeed it ever ends up existing.