What happens to those free Windows 10 upgrade after July 29, 2016?

Microsoft's ambitious plan to get Windows 10 running on a billion devices within the next few years depends to a large extent on the success of its free upgrade offer.
When the company first announced the terms of that offer last May, it literally included an asterisk and fine print. Those terms have changed slightly over the intervening months, but one element has remained constant: The offer is good for one year after the availability of Windows 10.
Here's the actual wording of the offer, as it appears today:

It's free and easy
Upgrade confidently - 100+ million fans have upgraded and are loving it. You'll have a free, full version of Windows 10 -- not a trial or a lite version -- if you complete your upgrade before July 29, 2016.
In fact, Microsoft's real goal with this upgrade offer isn't just to get its installed Windows 10 base to a billion. The long-term goal is to help close the books on Windows 7 in an orderly fashion before its extended support commitment ends on January 14, 2020.

What happens to those free Windows 10 upgrade after July 29, 2016?

Some of those Windows 7 PCs will simply be retired, of course. But what about those that are only a few years old and have more than four years of usable life ahead of them? For Microsoft executives, the prospect that hundreds of millions of PCs will still be running Windows 7 on New Year's Day 2020 has to bring back unpleasant flashbacks of Windows XP's messy end.

Scenario: A new "free upgrade" offer replaces the current offer.
Sometime in the first half of 2016, Microsoft plans to ship the next major feature upgrade to Windows 10, codenamed "Redstone." Members of the Windows Insider program are currently testing preview releases of the first Redstone builds, and the release notes for the latest build, 14251, intimate that new features will be arriving soon:
We're at the beginning of a new development cycle for our next feature update to Windows 10, and that means teams will be checking in lots of new code as they integrate their feature payloads.
In the new "Windows as a Service" model, Microsoft says it plans to deliver two or three new releases each year. So let's assume that Redstone arrives six months after the version 1511 update. That would put its release date in May 2016, which would give Microsoft about two months for one final push to convince holdouts to take advantage of the free upgrade offer before it expires.

And then July 29, 2016, rolls around. That's a perfect opportunity to brag about the success of the upgrade offer so far and to say it's been so successful that Microsoft is extending it for a limited time.