Marc Laidlaw posted a plot synopsis for Half-Life 2 Episode 3 on his personal blog. He has a simple substitution cipher for all the names, perhaps since he no longer works for Valve.
Reading it was very bittersweet. It is pretty clear by now that Episode 3 will never be made. So this is likely to be the only closure we get for Gordon Freeman. The story felt like something that fit well with the rest of the games, which it should, since Laidlaw worked on all of them.