Arcanaville mentioned something like this in another thread. Personally I'm unlikely to reuse my specific characters (reuse the names but not the characters) but I still kind of like the idea.
Several of my characters have backgrounds involving Portal Corp and/or dimensional exploration so I can definitely see them organizing a mass extra-dimensional evacuation complete with a group of heroes holding the portal until the very end. Or maybe Lord Harrandeous finally got his ship fixed and they all all piled onto that to explore the probability currents of inter-dimensional space.
There was an idea for a spin off for the GG group.
Where the Unity Vigil's orbital space station would be launched into space with as many people and heroes they could save. The idea behind that was the destruction of Galaxy City not being the end and the whole world was on the brink of being overrun/destroyed.
I have a signature, me.
Alright, so for many of us, we may just leave our characters with an ambiguous ending where they live happily ever after. Then the player goes off to a new game or something, never to touch their character again.
However, what of those who plan to bring their own character to another game? What could be the main reason for this mass migration of Heroes and Villains from Paragon City? So if I may suggest, that the universe we knew in CoX ended. Yup. Ended. Everyone dead. Well, except those who got out.
For those who want to have their characters live on in other MMOs, perhaps the game wide story could be a new universe, and with the lovely invention of Portal Corp, that is easily explained.
Now for those who don't like this and want their character's ending to just be as it is, a happy ending, then you don't have to follow this. This is really just a suggestion.