Normally even a single site single domain has at least 2 domain controllers. It is because Active Directory is at the heart of any organization where authentication takes place on domain controller. Domain controller houses the centralized database of users, computers, printers and other objects.
So lets say if one of your domain controller is not getting replicated and users are not getting authenticated via that particular domain controller and after the basic troubleshooting you cannot correct the problem, you can go for reinstalling the malfunctioning DC as you have a healthy DC in the same site.
I practically went through the steps given by Microsoft here. Pretty straightforward and lets you get back to normal quickly. In my personal view it is simpler to use this method than to restore from backup. But again you must have a healthy DC up and running in order to use this method:
https://technet.microsoft.com/en-us/library/cc785849(v=ws.10).aspx
Sajid Hanif's IT Blog 