Your Windows 7 license won't become invalid by updating to Windows 10. However, it is also part of your Windows 10 license, so you are only allowed to have one Windows 10 or one Windows 7 installation at a time with one key.
When I upgrade a preinstalled (OEM) or retail version of Windows 7 or Windows 8/8.1 license to Windows 10, does that license remain OEM or become a retail license?
If you upgrade from a OEM or retail version of Windows 7 or Windows
8/8.1 to the free Windows 10 upgrade this summer, the license is
consumed into it. Because the free upgrade is derived from the base
qualifying license, Windows 10 will carry that licensing too.
Your Windows 7 license will always be valid and will not be changed or
deactivated because of the upgrade to Windows 10: you'll be able to
install or restore Windows 7 again in case you'll need to do that
(provided that you've the Windows 7 installation DVD