When Brock Lesnar made his debut in the WWE, he was billed as "The Next Big Thing". He was young and ready to dominate the company for years to come. What do you think the state of the company would be if he'd been content to stick around? His departure was right around the time that John Cena was ready to break through as a megastar, which was going to happen whether or not he left. But would it have just been a Cena-centric focus for all those years, or would the spotlight have been shared? The move to PG was inevitable, but would having Brock on top throughout the 2000's have kept the product edgier than what we otherwise saw? What else do you think would be different, if anything.
Not much, I don't think. Brock was losing his "specialness" by the day at the end, and most of his aura now comes from his UFC association and rare appearances on TV. I think if he had stuck it out past 2004 he would have ended up just another guy or jumped to TNA for the easier schedule ala Kurt Angle.