Its too late for more power ups, and if Sasuke won then Gaara would be dead and we see from the sketches for The Last movie that he is still alive.
Is the movie part of the canon story?
What, where did you get this? Kishi is contributing to the script and character design.Its being written by Kishimoto and it is meant to continue the story after part 2.
So I don't see why not.
Also he keeps his movies at least partially in line with the manga, for example Jiraya was killed off and the Fourth Shippuden movie mentioned it.