u/Agreeable-Bass4646

Climate zone 4c. Tearing out this ceiling paneling and putting up fresh drywall. How would you handle the insulation here? It is a Dormer addition. Flat roof with a plastic membrane. Would it be best to tear out the old batt insulation and fill the cavity with closed cell or air seal the best I can then go back in with fresh batts or not worth the hassle and just leave it alone?