We’re already tumbling down that slope thanks to Disney. The house of the mouse saw fit to remove from canon the entire expanded universe so there is a precedent for undoing the films. Episode 9 explicitly contradicts the canon shown in earlier films as well. At least episodes 1, 3, 4, 5 and 6 have to be ignored if 9 is to be kept. Events in all of those earlier films are contradicted by what is shown in 9. 1, 3 and 5 all have shields working in an atmosphere while 9 says this is not possible. 4 and 5 do not allow hyperdrives to work in a gravity well but 9 does this at the start so JJ Abrams can fill his film with memberberries of planets we’ve seen before to try and convince fans that he has made a real Star Wars film. 6 showed the throne room on the Death Star to be at the top of a tower but 9 has it on the surface. Even the Disney published book about the backstories of Finn, Poe and Mary Sue Palpatine is contradicted to try and turn Poe into a new Han Solo. Of course there is far more wrong with 9 than just contradicting earlier films and books.