the blanket closure of schools put some children at risk
Indeed. But open schools are not the solution to child abuse. Children were abused before, during and after school closures. Children are abused and sent into school. Children are abused and kept home from school.
In Arthur's case, clearly being home from school did not help. But he would also have been home for 6 weeks in that same house during the summer holidays. Would they have sent him back in September? Would they have refrained from abusing him over the summer? As mentioned, he was reported to social services, he was reported to the police. Their failings to act appropriately are important lessons to learn from. We need these services appropriately trained and resourced to act when concerns are raised. Because whether schools are open or closed, concerns will be raised.
Linking his death to school closures and ONLY school closures in your OP is just grim.