Turning Slices into new separate TIFF documents in Photoshop

If you already have a way to export pngs from the slices just do that. Pngs are lossless so no harm done.

Then create an action that opens the saved pngs and resaves them as tiffs. Run it using file> automate> batch. Probably takes less than a minute to make the action and only seconds to run.

When it’s done delete the pngs.