The same way it always has
Microsoft will make money the same way it always has. It'll charge you for the initial version of Windows that goes on your PC and it'll charge business customers for support and software assurance.
The only difference between now and before is that Microsoft has finally worked out that the cost of supporting old versions of Windows is higher than the money it makes from the very small percentage of people who actually pay to upgrade an existing device.
How many people do you really know who have actually upgraded the Windows OS on their existing computer? How many people outside the tech industry? How many if we exclude Windows 95?
I'd bet the answer to those questions is "Not many", "Even fewer" and "Almost none".
Microsoft has never made any money out of selling OS upgrades to consumers because consumers never bought them. Plenty of people don't even pay for OSX upgrades and those have always been cheap. They have however spent a massive amount of money trying to patch old OS versions and ensure that their software is compatible with them.