No other bad actors can get it, but we don't know if it's already been found, and now that it's gone we have no idea what data is out in the wild. And as you note, we can't trust the companies to accurately report it themselves.
Another side is that with their database blanked, that will force more companies to explain their downtime or complete loss of data, rather than quietly secure it again and pretend nothing happened
no, that doesn't make sense if its only meow who found it. And since there is no way to know that, it does not make sense to mail a copy to hibp
Even a bland 'we lost parts of our data and we will have to start recovery processes. please stand by' is a signal.