What does this mean for us as Blizzard fans? Not much -- not only is Blizzard already running their own E3-like conventions (Blizzcon and WWI), but Activision Blizzard is apparently planning to hold a press conference on the first night of the show anyway. Blizzard's properties have enough gusto on their own to get press with or without inclusion in a big event like E3, and it's Activision's other properties that might have to worry about exposure.
As for the ESA news, who knows -- Activision Blizzard's pullout might mean a big shakeup in the way the videogame industry as a whole is represented, or (if no other companies choose to leave the ESA) it may not mean much at all. Time will tell.