SGA--Living it up in the Hotel Stargate Atlantis ("The Last Man" spoilers)

They can check out anytime they like, but they can never leave!

Well, at least not the city anyway. They city HAS to remain in the Pegasus

galaxy, on that planet--or SHEPPARD will not have a place to return to 
48,000 years into the future ("In the year forty eight thousand / One man
is 
still alive / Looking for a brand new day / Ain't letting nothin stand in 
his way-" erm, ahem, but I digress).

Of course by then, the humans will probably have inadvertantly (so they 
claim) unleashed some universal menace that wiped out everyone in the 
universe--again.

-- Ken from Chicago

P.S. Or at least the city (perhaps on autopilot, or holopilot) has to
RETURN 
to the Pegasus galaxy, to that very planet, for Sheppard to return.