Under JCT Standard Building Contract 2009, in a case in which practical completion is achieved with a list of defects attached, is it legally permissible for an employer to deduct liquidated damages until termination, if this is delayed due to insolvency?

Quite simply, practical completion certificates should never be issued when defects exist. In the situation described in the question, the onus would be on the employer to seek adjudication or arbitration citing the inappropriate issuance of the practical completion certificate.