NEC ECS: Would the Subcontratcor be liable for any costs for defects after the contract had been terminated by the contractor.

The contract was terminated by the contractor for a reason other than R1-R21 (contractors convenience)

The Contractor is using a defects list with costs to try and reduce the FA paid to the contractor with no substantiation, despite proof that the contractor completed all snags before leaving site

If the defects were attended to before termination then the costs are not genuine and could be challenged in Adjudication if that was to prove necessary.

If there are defects in work undertaken then termination does not relieve responsibility for those defects. It does however remove the right to rectify though any cost must still be reasonable such that costs are mitigated.

The real question you are asking seem to be fact specific and relates to whether the defects are genuine. Of course, if there are no defects then there is no liability. That said, it is not uncommon for defects to arise or be identified after a contractor has left site. It would therefore be best to review carefully the defects and require appropriate levels of information as to what they are, how they have arisen, what action is proposed and what the alleged rectification cost is. Pushing for proper detail is likely to flush out whether the defects are genuine or not.