Anyway I had two problems afterwards.
It logged me into a TEMP account so no config changes were saved and my files appeared to be all missing. They weren't, it just the shortcuts all point to the C:\users\TEMP\ directories. There's a few fixes for that one. Mine was checking the box that stopped OneNote from auto loading at start up.
After a reboot the start menu went away. The logo button is there but the menu doesn't come up. I found a site with a few fixed and tried them all in succession. I don't know which one solved it because I only rebooted after doing all of them.
So now I have 30 days to downgrade to Win 7 or forever hold my peace.
<backspaced off rant here />
Yeah, best of luck to them with this. It's not possible for them to put a condition into their EULA negating all legal rights. Imagine a completely ludicrous scenario: a Microsoft executive decides that they install an update that wipes your computer if it detects your version of Windows isn't licensed, and then another update accidentally causes your license to be invalidated. Then millions of computers get wiped. You think that licensing term is going to protect them from a class action? Think again.
I figured any attempt at a roll back at that point would have been worse than just proceeding. =(
Why not ask for the acceptance and then upgrade?
Do we know what data is lost when a rollback occurs?
I wonder how privacy settings are being handled, and whether harm is being done to those who are automatically upgraded.
I recall it was "Turn off Windows Customer Experience Improvement Program," which is disabled by default. There might have been other settings. (Search for security hardening guides for Windows to get a check list.)
What prompted me to check this was when Microsoft chose to willfully ignore the opt out setting they had handed us prior to the release date of Windows 10.. Let's not forget that either!
Edit: Oops. Double negative.
Imagine being Stephen Hawking. You wake up one morning to find you've been "upgraded" to Windows 10, and your assistive speech hardware no longer works. That will blow away anything in the EULA, as far as any judge is concerned.
The degree of irresponsibility required to pull something like this is simply staggering.