Any way it goes, as long as it's handled well, I think the fate of the Titans and what their influence will mean to the fate of the mortals of Azeroth will make for some of the most interesting lore in the series. As it stands though, I don't think their pattern of thinking is compatible with life on Azeroth is its current form. So they could be another enemy we need to worry about when we finally have the final fight with these overwhelming malevolent supernatural enemies of ours.
The only way I could see us taking the Legion, Old Gods and the Titans on would be if, when those forces began fighting each other, prominent casters among mortal races would be able to get us into individual fights between key belligerents (perhaps between two generals) and we temporarily aid one to defeat the other, then finish off the weakened victor. Not particularly honourable, but who cares about honour if the apocalypse can't be prevented! xD