The idea that had the Rams won the last couple years in St. Louis the league would have never allowed them to move to LA is a bogus premise as well.
The league wanted the Rams in LA whether they won or lost in St. Louis. And the stadium issue in St. Louis was pretty cut and dry. They could not prevent the Rams from leaving and the Rams and league wanted them to leave for LA win or lose in St. Louis. End of story.
If anything, Stan hired Fisher with the hopes he'd have them winning by the time they left St. Louis and could transition that into LA. He just didn't realize he was hiring a guy who had no ability to do that.