In a process of working on a different issue I discovered that a remote, not monitored site was not syncing properly for a while and as an effect we have a DC that is now "tombstoned" and is not syncing. The remaining DCs (corporate and one more site) are replicating correctly as far as I can tell.
As that one site is rather problematic to keep around and online reliably, I am thinking about removing that one DC, and possibly removing the site (not decided on the second part). I am not sure what the best procedure to follow at this point would be. Once the replication is broken the "graceful" removal/demotion process might not be possible, although I did not attempt it yet.
I am also not sure what the best practice is for separate sites like that: no local DC or possibly a RODC? That site has seen almost no usage in the last 12 months, and if even there are users/computers there it is a very limited deployment with under 15 devices. Site is connected by Comcast business broadband over hardware based always-on VPN - when actually "online".
All the DCs are 2012 servers, functional level is 2008 R2.