L4D is getting some new DLC on the PC and Xbox called "Crash Course", set between no mercy and death toll, so I imagine your helicopter crashes and you have to fight to the road at the beginning of death toll. Its free for PC, but you have to pay on XBL.
I personally have no problem with the sequel being out in just over a year. With the first game I got my moneys worth easily with the many hours I have clocked in with it. And really some fresh new official campaigns will be good, along with those new weapons