I'd hate to necro but since the last necro was six years after the previous reply I think I'm safe to share my take:
Others have said this, but Michael did way more in his lifetime than many of his fellow stars were able to do. I would say as an artist or a musician, he certainly may have reached his full potential. There was certainly more that he could do and wanted to share with the world, but the thirteen albums that are out are a big enough sample size for us to see what he could do. Career-wise he peaked with Thriller, obviously, and sonically I'd say he peaked with HIStory. But I don't think he ever peaked emotionally, be it through his art or through his personal life. That was due to a lot of factors, from his upbringing to media portrayals of him to reaching megastardom at 24 years old. I don't think he was ever allowed or ever allowed himself to live a normal and well-rounded life. Everything was either always too much or not nearly enough.
He was never able to age gracefully. Medical conditions aside, he tried his best throughout his life to channel youth and that just isn't healthy when you're over 50. I think that had he lived he might have finally gone into a bit of a retirement after "This Is It", maybe released a few singles or an EP every couple years, but quieted down, maybe married again and seen his kids grow up into their own people. He might've mentored younger artists or become a producer in his own right, hosted award shows, but constantly watch bright new faces rise up and make art like he always strived to do. I think he might have settled down and rested finally, not fading away into the background or into obscurity, but settling down to take his place as one of the founders of the music industry as we know it and one of the most influential artists of all time.
But because of his death he was never able to do any of those things. That's why I voted "no", because I think his full potential was to be a respected senior member of the music industry who would watch the world that he helped to make grow into bigger and brighter things.