If they don't make some sort of non-canon mashup level where you use the gravity and portal guns together to fight off zombies and striders I will personally chop Chet up and feed him to Gabe.
I just read an article that said Valve was looking to do more games like TF2 and L4D: A basic premise that can be updated hundreds of times and keep bringing in $$$.
In other words, enjoy never playing anything new in the Half-Life series without some kind of weapon being held to Gabe's flabby head.