So.. When is Mordekaiser going to take back the Immortal Bastion?

Not for a while. If he takes back the Immortal Bastion, aka the City of Noxus, that eliminates an entire nation off the map. In terms of lore, this cannot happen because it will upset the world that Riot is building.

He will probably get a lore event where he makes a atempt to take over the Immortal Bastion when he gets his vgu. Probably it will be another harrowing event where Noxus is at war against the dead. I'm really exited for an event with Noxus and Mordekaiser! Riot will probebly need to update all the regions and all champions lore befor they make an event as big as this though.

All in due time twirls heavy metal thumbs

...I like Morde, but only as a friend.