Just thought I should share this: http://fallout.wikia.com/wiki/Fallout:_New_Vegas_companions#Returning_Lost_Companions
It got me Boone back twice. Didn't work for ED-E but I'm hopeful Ill have better luck when I try again after a few hours.

Also watch out around Ranger Camp Bravo and Echo thats the only place I have lost companions.

Cheers

ED-E returns to Primm if you lose it.

Checked the Nash Residence and the V&V casino, no ED-E.

She is still in my party, I still have her perk, she just isn't following me anymore .

Not like the Rex thing where he just goes back to the King instead of the Lucky-38 when you dismiss him.

Do you remember where you last left ED-E?

I lost Fawkes in Fallout 3 (On PS3 GOTY Edition) once, and went back to where I last was and had to enter, and then re-exit an instance for him to load properly. Try backtracking and see what happens.

Relevancy to this in New Vegas: When I did a quest to get a follower to stand outside the Dino in Novac, I had to enter their house, and re-exit for them to keep following.

Last seen near Ranger Camp Echo she got stuck on the fence either coming or going, I wasnt concerned with it though since this elevator trick had already worked twice though.

Yes I've check the camp and Lucky-38.