[chris_johnsen]

I can only provide information from the perspective of another user, but I think I have the correct answers to your questions.

1. Stopping a backup will not harm the target volume in any way.
   1. It may leave the target volume in an inconsistent state with respect to the source, but the target volume itself will not be damaged ([i]SuperDuper![i] works almost entirely at the file level, so unless the OS or the hardware is at fault, SuperDuper! can not really damage a volume itself).
      1. The potential inconsistency comes from the fact that only some of the files will have been copied, so the rest of the files will either be missing (when using "Erase, Then Copy"), or old (when using "Smart Update").
2. If you make a later backup using "Smart Update" (which is, as far as I know, the only meaningful way to 'resume' a backup with SuperDuper!), it will skip any files that are still up to date.
   1. I can not say that it will not take another 48 hours to 'finish' the copy, but if there are no changes to the files that have already been copied, then it should be able to get past those and start copying new files relatively quickly.