hi Mahmoud,
As Rene has explained on the lesson, when the evaluation license is expired the feature(s) won’t be disabled and Cisco expect its customers to behave and not take advantage of it.
With reloading a router which has an expired evaluation license, you may get an output on the router like this:
Router# reload
The following license(s) are expiring or have expired.
Features with expired licenses may not work after Reload.
Feature: uc,Status: expiring, Period Left: 4 wks 2 days
Proceed with reload? [confirm]
So it is always recommended to purchase the PAK from Cisco once the evaluation license is expired to keep the feature active.
Hope I could answer your question.