What happens when I reload a PC/"Reserve" Windows 10 free upgrades

Two questions:
1) What happens when I reload my Windows 8 PC after the free upgrade expires?
I have a Dell desktop that came with Windows 8 (or 8.1?) home. I did the Win 10 upgrade and then used my Win 8. Pro upgrade key to upgrade to Win 10 Pro.
I have created a Windows 10 ISO and I know the generic key (VK7JG...) is the one used. If I need to reload the PC after the free upgrade, will I be stuck with Windows 8 again or can I use the ISO and key to upgrade again? If not is there a way (short of a disk image) to make sure I can upgrade?

2) I have two Windows 7 licenses (Pro and Ultimate). Is there a way to reserve the Windows 10 upgrade with them, like for instance installing them on a virtual machine? This of course would tie into question 1 possibly if and when I need those installations. I could of course (depending on the virtual machine I think) convert them from p to v at some point as well. Any recommendations on which system (Virtual PC, VMWare, etc.) to use if that's the case?

alphanumeric said:

If you've done the free upgrade, that PC should now have a digital entitlement for Windows 10. Go to Settings > Updates & security > Activation. It will tell you there. If it has a digital entitlement you can clean install/reinstall Windows 10 any time you want (even after the offer expires) and activate with the digital entitlement. Just install the same version that's installed now, and click skip when asked for a key.

Thanks, so does that mean they have some kind of database that has our HAL information and to check with for future reloads? How else would they know it was ok?

alphanumeric said:

It pretty close to how its always been. A digital fingerprint if you will of your hardware is created when you activate. A hardware ID. It's stored on the activation server. When you reinstall and go to activate, the activation server looks for a matching digital ID for your PC. If one is found, it activates. If it doesn't match, it won't activate. In the past this was also tied to the product code used to activate. Now, with a digital entitlement it isn't. The digital entitlement uses a generic key. Installing with that key will not activate if there is no digital entitlement on record for that PC. If you do upgrades to your hardware the ID gets updated to match. Like in the past, you can pretty well swap out anything except the motherboard and not have activation fail. Just don't change to many things all at once.

https://support.microsoft.com/en-us/...-10-activation

Thanks, so installing the unused Windows 7 licenses on a Virtual PC/VMWare/etc. and upgrading would not really do me any good.

At least I know how the system works. I know in the past when I've reinstalled an OS a few times (replaced the hardware and activated it again) I have had to basically click a box (and once or twice call) to say that I am only using the license on one PC. I wonder if they would go for something similar so I could use those licenses...

alphanumeric said:

I don't do anything Virtual PC wise. I just never bothered to try it. In the true spirit of the free offer, I don't think Microsoft intended it to be done on VM's. I'm not judging, just my opinion. I have no idea if it will work, or be worth all the effort. Just my 2 cents.

That's fair enough.