I think with all the Doom and Gloom talk, which may or may not be warranted, I think it may be wise for this community to have a contingency plan.
While other players will be all "QQ my City" or "OMG but I am the original "Leetownz" I don't want a -1" we will have to be talking about how to explain, in character, how all these new people suddenly show up.
What happens when suddenly there are two Security Ministers for Newland? What happens when suddenly a new Omni-Pol shows up working high profile cases no one has heard anything about before?
I think it should be handled using a Multiverse concept. Atlantean sends a forward scout through a portal to Rimor, pleading for immediate aid and seeking to petition our world's ICC for asylum, if our world has an ICC.
In Atlantean the alien's invasion plans were set in motion by the losing of a particular battle which the Rimorians won (perhaps the killing of the Art Commander, Rimor Represent!). This allows the Atlantean Omni-AF contingent to shuttle intelligence of where the aliens are staging and waiting for their opportunity to strike. With the intel the Humans will be able to preemptively strike and save the world.
Rimor is saved due to the Atlanteans, Asylum is granted, and an IC explanation is made available to the playerbase to use.