Why not check the Microsoft website for information on the length of time that it’s free.
I posted what l read, which came from a MS Rep who said it’s free for the length of the license.
Do you work for MS?
No, but I've answered questions like yours dozens of times in the last few days for family, friends, etc...........
If you doubt what I said, you're free to google "how long can I download Windows 10 for free?" and you'll find the same answer.