At the final part of this mission, Miraak does not appear at all. Could someone please help me? I had look around on forums and tried a script in the console which bought the dragon into play, but I could not tame it once I finished it's health bar. Please help.

Check the http://www.uesp.net/wiki/Dragonborn:At_the_Summit_of_Apocrypha section. So much can happen here. Hopefully you have a good save beforehand that doesn't set you back too far.