What happens if you disagree with the terms and conditions after an update?

Once you are doing an update, after reboot, the device is asking you to agree to updated T&C.

If you disagree, does it revert back to the previous iOS?

The text is saying that if you don't agree, you shouldn't use the device and can return it within a specific time frame.

But what if the device is not new, and you click on disagree. What happens next?