The short answer is that the half speed masters will preserve quality to the max and will be comparable to the actual master tapes, unlike the original vinyl which were far inferior but alas was the acceptable standard at the time. As a recording artist, listening to the vinyl was wholly depressing after hearing it ‘perfected’ in the studio. Half speed vinyl would have been a much more acceptable form of mass production.
The master tapes were not damaged or lost. However multi-track tapes were irreparably damaged, which means the music can not be remixed.