Yes, subject to the deadline for presenting claims to the estate of the decedent (within sixty days of publication of public notice).
If a timely claim is filed against the estate, Article 9 of the Uniform Commercial Code allows a defense in to deficiency claim debt such as this one that the method of the sale of the collateral was unreasonable, but this is rarely a complete defense and is rarely successful in practice. Lack of notice would not automatically invalidate the debt (and the instrument creating the debt probably waives the co-signers right to notice of a sale contractually).