So apparently..Valve is going to kill off one of the original survivors from the first game which will lead up into L4D2..
The character will sacrifice themselves so the rest can move on and make it out alive and from there they original(3) who are left meet up with the new survivors..
Of L4D2..

Here's the article posted on Destructoid.

"The latest episode of GameTrailers TV premiered last night and host Geoff Keighley spoke with Valve's Chet Faliszek where he revealed that some bad times are in store for the Left 4 Dead heroes. The Passing's newly revealed tag line, "Nobody Lives Forever," foreshadows what's to come.

With the upcoming Left 4 Dead 2 DLC, you'll be encountering only three of the Left 4 Dead survivors. Yes, one of the original four will be killed. With the Left 4 Dead DLC, you'll be playing through the events that lead up to the death and someone on the team will have to sacrifice their life so the rest can move forward.

Valve will also be releasing a couple of comics between the adventures. The comics are based on the two DLCs and present an idealized version of what happens to the survivors.

Player choices are becoming more and more integrated with games, but I don't think any videogame has done something to this level yet. You and your team will have to decide amongst yourselves who will have to make that ultimate sacrifice."

So..who do you think will die..?
I honestly think Bill will die considering he is the oldest..and usually the old guy ends up dying because he wants the young kids to live..and yatayata..
And will you be getting either DLC of "The Passing"? for L4D or L4D2?

Bill, maybe, but i would put my vote on him...