When you say "throw away Windows 10 Pro subscriptions", what do you mean exactly? Do you mean just not using them (by running Linux instead), or do you think if you install Linux you'll lose the licenses?

If the latter, the activation/product key is (usually) stored in the firmware of the machine, so you can reinstall Windows in the future and it'll automagically be activated with Windows 10 Pro again (you don't even have to input the product key). To check, follow this guide, and run this command in an Administrator-level PowerShell:

wmic path softwarelicensingservice get OA3xOriginalProductKey

If the command returns the product key then you're good to go.

On units built by major manufacturers who have volume OEM licenses from Microsoft (Dell, HP, Lenovo, etc.), Windows license keys are burned into the BIOS. So you can always reinstall Windows later, and it will retrieve licensing information from the unit's bowels... Just remember to leave the license key field empty when installing; this will prompt the installer to search for a license key stored on the system.

Also, Dell has something called OS Recovery Tool. You can install it on any Windows machine, then enter a service tag number for a Dell PC, and the tool will download a Dell-tweaked version of Windows for the specific model associated with that service tag and make USB installation media from it...