Q: Aperture help! (Reposted)

They should not have been removed, so it's likely they were relocated.  Have you searched the list in the Keywords HUD for any of the missing keywords?  That's the first thing to try, imho.

Bring up the Keywords HUD ("Window ▹ Show Keywords HUD"), and then use the search field at the top of the HUD to see if any of the missing keywords are still there.

Have opened all disclosure triangles in the Keywords HUD?

You may have dragged the missing keywords onto another keyword, when you tried to drag them,  and created subordinate keywords this way:

What else have you tried?

Can you find an Image that you know had had one of the missing keywords applied, and check whether it is still there?

The next step is to repair your Library.  This usually helps with UI inconsistencies.  It shouldn't cause any problems, but the standard precautions apply:  never use any computer file without having a back-up. 

Details for running "Repair" are on Apple's Aperture trouble-shooting page.