If you had win 10 on the device, you can still install it again. You don't even need to know license key as its all stored on Microsoft servers. All you need is a USB to make the installer again. I doubt you really want to roll back to Vista now.
On another PC, download the
Windows 10 media creation tool and use it to make a win 10 installer on USB
How is win 10 gone? What os is on it now - how can you try to get internet without an OS?