Time to restore your file from a known good backup, then replace the images through the GUI.

Do note that replacing PNG and JPG files with TIFF files is liable to greatly increase the file size and, even so, may not result in a noticeably better printout. For starters, few people could pick the difference between an image printed @ 300dpi vs 600dpi or even 1200dpi in an ordinary document and, if you allow Word to apply its image compression (which you might need to do to keep the file size below 512Mb - Word's upper file size limit), the most resolution the images will have is 220dpi anyway.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]