Even without all the sequels and prequels Star Wars would still have been endlessly referenced for decades after the 2nd movie.
Not necessarily. Being able to stick the landing is hugely important for a series’ legacy. Game of Thrones disappeared from conversation after its disastrous final season, but would probably be fondly remembered if it had been suddenly cancelled after season five. If ROTJ had been a similar dumpster fire, Star Wars might have gone the same way.