I wonder if the loopback shutdown is a red herring. The "files nis" switch around seems more like a clue. Perhaps some outstanding RPC after the network shutdowns (ethx's are down before the loop, no?)
I'd try playing around the shutting down these bits manually in various permutations leaving the system running to see if it hangs. I have SL6.x systems running NIS without problems but then I did not reverse the "files nis" in nsswitch.conf.
