Although the Olympian crystal may have been a way for the writers to say 'don't expect Robin back', I also in-universe refuse to trust the word of Hades. If it's a bad thing that Robin no longer exists, then maybe we can tell ourselves it's not true. After all, Thanos was wrong when he said it. With Belle's dad the worst thing for me is he denies her choices. It's like locking your kid in the basement until she agrees to break up with her boyfriend.