The difference between Prince & MJ - in regards to the timing of their deaths is that Prince productivity and output level is as high as ever - with 4 albums in the last 18 months and he was working on more
Also Prince can posthumously surpass MJ
I didn't want to say this yet but Prince has the potential to be the greatest posthumous artist of all-time - and I would suspect that his unreleased material is a lot more finished and put together than any other artists a majority of which would feature less collaborators and sampling so there will be very little red tape on getting his work out in it's original form
Keep in mind how large his catalog is now, it's been said over 70% of his work is unreleased. Conservative estimates say there's about 2,000 unreleased songs