While there is one real conclusion to the story, as evidenced in the previous DLC "The Passing," players will have the opportunity to re-write history and select which team member will fall in "The Sacrifice." It won't change the franchise's canon, but it'll make you look totally badass.
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"The Sacrifice" will be available for free for PC users and for 560MS Points ($7) on the Xbox 360 when it launches on October 5.
While Valve has kept silent on a previously reported Mac version of Left 4 Dead 2, the trailer lists "OS X" as one of the DLC launch platforms. Looks like it's happening after all.