Looking at past reconstructions of films (live-action), a lot of the more complex ones nearly always had at least minimal directorial assistance. Napoleon was reconstructed by Kevin Brownlow while consulting an elderly Abel Gance. It was another case of a film with a lot of existing footage left out, but also a lot not meant to be inserted back. Lawrence of Arabia actually had David Lean knee-deep in the project - he made new editorial decisions that time-constraints didn't allow back in 1962. He even directed the voice re-recording needed due to sound recordings being lost over time. Spartacus was restored with minimal input from Kubrick (since he apparently wasn't that fond of it since it was basically a "for hire" project), but he did answer stuff via fax.
However, the ones hacked and gutted rarely do. Orson Welles couldn't offer input on Touch of Evil (only a 40 page memo outlining changes he wanted to the studio release) and obviously couldn't for The Magnificent Ambersons. The latter is further hurt by the fact that we recently lost Robert Wise - the original editor (and supplementary director for some re-shot footage).
It's beating a dead horse, but it wouldn't even be that kind to pull Williams back into this. If he's working on something new, the last thing he needs is to hold off on yet another project so he can work on another. It wouldn't be fair to get "Thief" at the expense of having an unfinished new film. Even if he wanted to give advice, would Williams really have the same viewpoint as he did in 1992? He was always working on a little bit of the film from the 1960s to the early 1990s. I can't imagine how tough it would be to just go back after 15 years hiatus.
That being said, the money spent properly finishing it would at least make it a prestige project. Do you think Disney has made any profit off Destino? At least it could get a limited NY/LA release and qualify for the Best Animated Feature Oscar. It would probably win that, as well as sweeping the Annies.
Fox spent $5 million restoring "The Black Swan" which I hadn't even heard of until the DVD came out. They're selling the disc for $14.98 SRP and will probably never make back just a tenth of that cost. But it's restored and preserved for posterity's sake. Disney could try out a preview screening of the september workprint (perhaps revised for better quality) to guage audience reactions. One idea could be to work out something with Turner Classic Movies to run Who Framed Roger Rabbit and the workprint back-to-back.
If Disney starts a completion/reconstruction now, it doesn't matter if they make money immediately. If it's in the can, it can make money a decade or two later. It worked for Fantasia, Bambi, and Alice in Wonderland... Even without Richard Williams being involved, just the available bootleg materials have given us a really good idea of how it should all be put together correctly. Now imagine access to every bit of existing material (film reels, pencil drawings, cels, backgrounds, storyboards, layouts, voice and music recordings, sound effects, timing sheets, etc)!
Even without Richard Williams participating, it's not like the film could be made any worse than what's already out there.
I'm overly idealist and optimistic, but Disney deserves all the support they can get. I thought a Variety ad would have been a way to get people interested and encourage Disney. No confrontation or ill will like Gilliam's ad. But if it would appear to be confrontational, that's that last thing we need.