Disabling the Unofficial Skyrim Patch will be your friend. I spent at least 4 hours trying many of the tricks suggested killing all the dragons, killing none of the dragons, hiding to get Miraaks health up, restarting the sequence, e.t.c. all with the same result...Miraak stuck in ethereal in the fountain. I disabled the patch, loaded my save game with 3 dragons alive, and the Miraak sequence went down as advertised on the first try. He recovered from the ethereal loop, killed all 3 dragons, captured the 3 souls, and then met his demise. Mission accomplished. Good luck.
