Recently we had the task of performing a few Uninstalls of Civil 3D 2013 and the order of Uninstalls shown below seems to work successfully. This is not the only order that will work, but there are certain things that must occur. For example, you have to remove the Storm and Sanitary Analysis Plug-in before removing the Storm and Sanitary Analysis component itself.
2014 versions and later include an Uninstall Tool, which is noted in the Twitter conversation linked to above.
