We all know from our favorite haunted house (and previous ES games) that Molag Bal is still alive and kicking.

But is this the same Molag Bal? Do you think they'll pull a Sheogorath/Lich King, replacing one god-character with another?
Or will he simply be banished to his own humble plane of Oblivion?

He wouldn't need to be destroyed, just kicking him back into Coldharbour will suffice.

I say we send the anchors into Oblivion and have them duke it out against each other once it's pulled into Coldharbour.

That would probably be the only thing that would actually anger me. It's a basic fact of the Elder Scrolls universe that Daedra cannot be destroyed, by any means or by anyone, only defeated and banished to the Waters of Oblivion to eventually find their way back to their home plane. Not to mention that, as you mentioned, Molag Bal's still doing his thing in the Third and Fourth Eras, so...