The Holloywood Reporter has a synopsis of the 500th episode:
The Simpsons' 500th episode, "At Long Last Leave," centers on the Simpsons family getting evicted from Springfield and join an off-the-grid community outside of town. But when Homer and Marge try to return to Springfield, their friends give them a hostile welcome.Fox has already announced that the show has been renewed for two more seasons, ensuring it will air on television for a record 25 years, longer than any scripted show in history. The Simpsons premiered in 1989 (I saw the the very first show when I was in college) and George H.W. Bush was president of the United States!