>> "It looks like I would need to be calling IsGenuineEx and forcing a server call daily by setting daysBetweenChecks to 1, until I detect that they have renewed. "
Nope, we cover this in-depth here:
https://wyday.com/limelm/help/license-features/#change-datetime
https://wyday.com/limelm/help/license-features/#change-field-read-new
>> "What happens when the software stops working because they didn't renew and they call and do a renewal and want the software working again right away? Any way to force the software to update the license other than deactivate/reactivate?"
Yes, covered in the custom license fields docs -- see the links. Give them a prompt so they can renew.