This is a great post from Mark on what the present penalties are for failing to renew Sage maintenance. This was taken from a reply Sage sent to a customer who did not renew.
As always double check the current market conditions before quoting it to a customer as Sage seems to change their penalty computations from time to time.
http://community.90minds.com/2013/05/29/what-happens-if-i-cancel-my-sage-maintenance-plan/