Apparently it is still possible to activate a Windows 10 update using a product key from an eligible Windows 7 or 8 version if you have installation media. But clicking the annoying little icon on your computer will take you to an offer has ended window. If this is an oversight, there is no telling how long it will remain.
 
http://www.zdnet.com/article/what-happens-free-windows-10-upgrades-after-july-29-2016/?ftag=TRE17cfd61&bhid=22965424546014440578610366214509