I'm very pleased to read such a thread about the editing team, something I've not looked at. I know I read someone's post elsewhere that the producer, Gary Kurtz, may also have been a massive factor in the success, and he bailed after ESB! He went on to produce 'The Dark Crystal' and 'Return To Oz', two of my favourite fantasy movies.
I had a look at iMDB at Richard Chew, Paul Hirsch and Marcia Lucas. Marcia stayed for all three, but Chew bailed after ANH and Hirsch after ESB. All three have worked on superb productions elsewhere (including, collectively, 'Alice Doesn't Live Here Anymore' and 'Taxi Driver' (Scorsese), 'One Flew Over The Cuckoo's Nest' (Foreman), 'The Conversation' (Coppola), 'Falling Down' (Schumacher), 'The New World' (Malick)) and never worked with Lucas again.
Also worth remembering are John Dykstra, Ralph McQuarrie and Ben Burtt (on sound!
).Burtt is the only one of the people mentioned above that has stuck with Lucas right up to the present. All the others had bailed by, or just after, 1983. And all of the people mentioned had a pivotal role in creating what has become the Star Wars universe.
It does not (and has not ever) rested upon Lucas alone.