I can't imagine that we would lose the Tower and it's population. It being there is such a central part of the overarching story and there are still very many loose plot ends hanging around in that place. As long as guardians are still defending the Last City I think that it will be our central hub. Why would the factions and staff of the place would suddenly change when they have had all this character development? It's like you want a new game in a new universe. Like screw it lets just rewrite the whole plot and start again...