Yeah, just on off-the-cuff calculations, say 30 million copies across all platforms,could be as high as 40 M, but PC is only 16-17 M. I'm not sure what cut Mojang gets from the non-PC versions after you take out the development costs and Xbox/PS platform royalties, but let's say that Mojang grossed about $20 per copy overall. This includes he alpha and beta sales that were for under $20 averaged with the higher costs now.
This comes out to $600-$800 M before taxes, so after you factor in Minecraft Realms monthly fees and any income from Scrolls, you're probably somewhere around $1B in sales. I'm pretty sure there are more than 2 employees with equity in the company, and when you factor in Swedish income taxes, Notch is clearly not a billionaire in dollars.
It's worth $2B to Microsoft, because they can milk the Minecraft cow for at least that much by merchandising paraphenalia and movies, Minecraft Realms is also an ongoing cashflow. Oh, and I bet they institute a monthly fee for Minecraft Server.
Apart from the money, I think Notch is really selling because he's sick of the BS of running a company: Bethesda suing them over scrolls, parents suing them over exploitative MC servers....etc.