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dcpyke - if the .opf are corrupt and cannot be recovered by OS or third party tools, then they're gone.
If they can be recovered in some shape or form then you could open them with a text editor that can deal with LineFeed only line endings (essentially that means most anything - except MS Notepad) You might then be able to eyeball the data and re-enter it.
To avoid a recurrence of this 'down the line' see ==>>
How do I backup calibre?
BR