This is how it is supposed to work. At the 50% mark (in this case 3.5 days), the workstation checks in with the DHCP server and verifies that it can keep the lease (if it can, the timer is set back to 7 days again). If the DHCP server doesn't respond, then it wait another 50% of the remaining time (1.75 days). At that point, it again checks with the DHCP server. If it succeeds, then the timer is back to 7 days. Otherwise it waits another 50% of the remaining time (I think). Anyway, at the end of the 7 days, if the DHCP server doesn't respond, then the workstation will have no address.
