darjr
I crit!
Both in the Great Wheel and the imposed 4e cosmology in 4e FR:
Resurrect Tiamat? She was never dead...
And bring her back from the 9 Hells? She has always been there voluntarily...
I think in the Dungeon 4e adventure path the players kill Tiamat and banish her to the 9 hells, she can't leave.