According to Lucasfilm, the negatives were permanently altered when the SE-added/changed scenes were spliced in after the "restoration." That's why they released the 1993 LD transfers in 2006 instead of a new transfer of the pre-SE versions - they don't exist anymore. So it's not that they're "destroyed" so much as "permanently altered."

That's really a load of bullshit, since, even if they did that to the negatives (I have my doubts, but wouldn't be surprised in the slightest to discover that this was true), there's still several three-strip archival interpositives of the pre-SE versions - one (for each film) in Lucas' personal vault, one in the Library of Congress, and I believe one in the UK's equivalent of the Library of Congress, among other places. Any one of those would be of high enough quality to make a very good 1080p transfer, and definitely a very nice SD DVD.