Almost certainly won't. Movies never impact the main anime plot; they're always self-contained adventures (usually with a tie-in episode) and for years have always had a Mythical to shill.
Nobody knows, nothing so far has been hinting to that, but maybe. Or maybe not.
So far, yes. There are a couple of things that remain constant, like Gladion having Null and a passing reference to Lusamine, but everything else has been changed.