If you run out of spare sectors on the disk, your data is lost forever, as far as I know.. Even though your sectors are still readable, if the drive detects that the spare pool is filled up, it refuses to do anything to the disk.
Talk about excellent design?
The place you got tip from (trouble in paradise) is a good source of info on Zip drives and the click of death syndrome, perhaps you can find some info on salvaging your data there?
If all else fails, then something like Norman Ibas can restore your data, but it's so expensive that the data needs to be very valuable for it to be worth paying for.
I wouldn't trust a Zip drive for anything.. I do my backups on DLT.
