I was recently tasked with removing a server from a farm where the virtual server no longer existed, I knew that the best practice was to Disconnect the Server and uninstall SharePoint on the server itself. But what happens if there’s a catastrophic failure on the server and you can’t follow that process? Simple.
The following applies to SP 2010/SP 2013
Browse to Central Administration > System Settings > Manage Servers in this farm On this page you will see a list of the servers in the farm Click Remove Server You will receive a prompt but as the server is no longer available the only choice to remove the server is to click OK. What’s really important here is that Best Practice is not to do it via this method but because your server has been removed you have no choice but to remove the server in such a way.
It is recommended that you uninstall SharePoint Products from the server, rather than removing the server from this page. Because the Remove Server operation does not delete information from the server, such as any registry keys that were set, use this operation only when the server is no longer available.
Click OK Refresh the page and the server will be removed. Voila done! Easy as.