The third issue of the comic is out! We are one week away from the final chapter and the DLC. People have been asking about what is canon (the official story) the game or the comic? The Comic is the official version of events, but Left 4 Dead has always been about organic story telling between you and your friends, so we wanted to not force you into one story line in the game. You get to choose the ending and see how it plays out.
We will have more information on the DLC later this week.
Source
The third issue of the comic is out! We are one week away from the final chapter and the DLC. People have been asking about what is canon (the official story) the game or the comic? The Comic is the official version of events, but Left 4 Dead has always been about organic story telling between you and your friends, so we wanted to not force you into one story line in the game. You get to choose the ending and see how it plays out.
We will have more information on the DLC later this week.
Source