I just did that quest today. The falmer with the crystal is in the Mzulft Aerodrome area in the large room with the three doors leading off of it.
You could check to see if the dungeon says "Cleared" or check that his body hasn't got flung somewhere out of the way when you killed him. There are three falmer in that room, so you might have missed him when checking the corpses.
Thanks. Ill check to see if it says "cleared" on the dungeon. I did not think of that. I considered that his body may have gotten flung out of sight so I tried loading a previous verson but it does not result in any Falmer boss caster. There are 4 Falmer in that room; 2 nightstalkers (caster) and 2 regular falmers, but no boss. This is the case no matter how many times I reload just before entering the Aerodome.
And to the previous poster, regarding the marker, thank you but as I stated there is no marker no matter if I have the quest selected or not.... This has happened on one other quest for me before. When I click the quest in the quest choice screen or press "show on map" from the quest, it just makes a sound like "bump" not the usual "click" and it does not show up on the map. Even if I leave the dungeon and go to skyrim (from the observation deck) it still doesnot show a marker.
Please keep the ideas coming as this quest is bugged for me. I will try to redo the entire dungeon tonight and hope for the best...