The fact is that Marvel owns the rights and they would have proceeded with the film had Wright dropped out, if they so desired. Whatever work he had completed on AM belonged to them; they could have used it or simply hired someone else to go forward. Wright's foot-dragging is the reason for that six year delay, from all that I've read. That delay prevented Ant-Man and The Wasp from being in The Avengers. In The Wasp's case, Whedon definitely wanted to include her, perhaps leaving Ant-Man for the solo film, but that got shot down.