MIDahlias I hope someone here has great advice for you!
I think I might toss tubers that feel like grapes, but that’s coming from a novice! I’d be more worried about the grape-consistency than the skin peeling off. At the same time, never say never with dahlias. Keep an eye on ‘em for a few days, perhaps they’ll bounce back? You could try lopping off the majority of the soft tuber and potting up right away to see if they’ll sprout for you for cuttings?