I ran into the same glitch that occurred on the Xbox 360 version. Miraak would warp to the center of the map and stay etheral. None of the original solutions seemed to work, so I shouted Bend Will at Sahrotaar and slayed him. That took Miraak out of his state and allowed me to whoop his arse again. I used an unenchanted daedric mace to whittle down his health, as I've read hitting him with too much power is the cause of the glitch.
Hope this helps those who got stuck.