I took the silver dragon's quest and went to the Drow City. I did all the Drow Quests and got the eggs. I went back and killed the Dragon. Then I went and killed the Drow. How do I get out of Underdark now?

I guess you're stuck!!!!!

Actually maybe not. Go to the Kuo Tua dungeon, it lies roughly southwest of the svirfnebli village, just keep searching along the edge till you find the entrance. Go in and clear it out There is an exit to the surface there guarded by a bunch of drow, you should be able to use it.