4th Smash Bros? eventually
Question is... will it be with... or without Sakurai overseeing the project.
Iwata said to Sakurai in some interview:
I had considered what I would do if you turned me down and decided that I would need to take the existing Smash Bros. title, Super Smash Bros. Melee for the Nintendo GameCube, and try to make it Wi-Fi capable while preserving as much balanced game play as possible in the event you didn’t want to get involved. Maybe it’s more appropriate to say that I realized we wouldn’t be able to add any new elements to the game without your help.
So yeah, brawl would exist without Sakurai; as there probably will be more down the line... but, Sakurai being free and motivated to do a smash next time around is not a given.
I wish Nintendo bought Sora, ltd and gave them creative liberty though.