Removing and reinstalling Windows 7

There is a roll back option for returning to the previous OS after the upgrade to Windows 10 but this only lasts for 30 days from upgrade.

The other thing is that after the upgrade is past this 30 days cut-off date the windows 7 licence will be converted into a digital entitlement so will not be valid for use on a re-install.

If you were using Windows 10 Pro I would suggest use of Hyper-V to run a virtual windows 7 for support purposes, (you can always run this for the 90 days at a time (using the extended trial ) ), maybe a 3rd party Virtualisatrion package would be an option.

There is always a possibility that that sort of install will work, if not you can call Microsoft, explain your circumstances, (which, to me, seem reasonable and beyond your control), and they may re-enable your key or even supply a replacement.

If they refuse then you would either have to run the Windows 10 (the digital entitlement is on the MS servers for the system),and a virtual Win 7 or you may have to obtain another key

You can still download a legal copy of Windows 7, use one of these methods:

1. Download Windows 7, 8.1 and 10 ISO Images from Microsoft

2. Download Windows 7 ISOs, Legally and for Free

3. Microsoft DigitalRiver Mirror (Technet)

The first requires you to open the Developer Console in Firefox or Chrome and paste data from pastebin.com into the console and press enter. This has to be done every time you want to use this web site to download from.

The 2nd is a German torrent download site with verifiable MD5 checksums for each of the available ISOs.
To download Windows 7 using a torrent file, we will need a torrent client.

The 3rd downloads a torrent from technet mirror corenoc.de.

Any torrent client will work, though, but I recommend qBittorrent. All the others I've looked at try to install
other garbage along with the torrent program so avoid them.