Comment 2 for bug 137408

Subscribers to originals being broadcast messages from duplicates is bug 106162. Once that is fixed, the benefit from corraling any is-this-really-a-duplicate discussion in the duplicate report itself will increase to its proper value.

I think your #4 would make the effect of undoing a duplicate marking either surprising (if it returned apparently-removed assignees to their positions) or lossy (if it didn't). As for whether any of the data in a duplicate report is important, it's important if it turns out not to be a duplicate after all.