Armor Lock isn't overpowered. You just suck at Reach :)
Reach isn't bad, you're just a BK :)
For my gamertag, look up "Ghoulishtie"
Ok, heres proof to you that they WONT be on it.
New Mombassa was built above the ground that covered the giant forerunner construct that creates the portal when the keyship is used.
After Regrets carrier goes into slipspace, and MC/johnson/keys follow, it doesnt destroy the city completly, just damages it.
So since the city is still intact, the UNSC (mainly ur ODST's) have to fight off the remaining invading covenant from the damaged city.
No one knows what happens to the city fully, but in Halo 3, the city is completly gone, and the forerunner construct is fully revealed, thus, no New Mombassa. Heck, they even say in Halo 3 (forgot who says it in game) that it was under the city!
So ya, sorry, but no flood.