In the scenario we have 3 DC's
When one of the DC is rebooted within normal working hours (Guess it is the same out of working hours - have not tested that). Users who has locked their computers, will not be able to logon when they return to their computer again. Computer has to be rebooted before they are able to login again. DC's are 2008 R2 and computeres are Windows 7.
Best regards,
Thomas