Are there going to create left 4 dead 3

That is yet to be seen. Left 4 Dead was a HUGE hit, Left 4 Dead 2 was good, but did not get as much attention as the first game. It is possible they will try to perfect another one to match the first, but usually if they make a 2nd game and it doesn't do as well as the previous, they will give up and move on too making a totally different game. I was a fan of the 2nd game, but I just don't see them finding the motivation for a 3rd.