Perhaps better done entirely single server side?
Although syncing servers does open up a lot of possibilities, sometimes restraint is rewarding.
In the case of switching servers to do little more than switch maps, perhaps smart server configuration would be a better option than dis-then-reconnecting all clients during a mission.
Just my twopenny's worth :-)
That said, co-op missions running simultaneously on different maps would be an obvious awesomeness; with progress on one map affecting the circumstances on another etc.
Interesting extension to the platform :-)