Will Windows 10 be activated

What about this scenario:
1. Was running activated copy of Windows 7
2. Performed clean install of Windows 10 from USB boot
3. Cannot activate Windows 10 because upgrade was not performed from Windows 7

What if I do this:
1. Disconnect primary drive and attach a different drive
2. Clean install Windows 7 and activate
3. Upgrade the drive to Windows 10 and activate
4. Disconnect this drive and reattach and boot from the primary drive

Will Windows 10 be activated or allow me to activate now without reloading what I already have?

That should work ok. Microsoft wants to see an upgrade from activated Windows 7 or 8/8.1 to Windows 10 and record you system details on its activation database. After that, a clean install should activate successfully. Swapping in a clean install of Windows 10 on a hard drive created on your current system should work after the above upgrade.

I would think it would work. After you are all completely done, if Windows 10 doesn't activate automatically, open an elevated command prompt ("Run as Administrator" command prompt), type slmgr /ato

That will run the online activation

then type slmgr /xpr

That will tell you if you are activated and if/when activation will expire.