Further, as you implied, if the seller received compensation significantly higher than the true NPV/MTM of the equity, the difference may likely be subject to legal claims even if Zhoutong acted in good faith if the current owners convinced Zhoutong to sell his company so the current owners can strip/steal all the deposits (as the non-disclosure of the ownership transfer was proximate cause for the loss).
This is possible. Even if Zhoutong received a fair price, he could still theoretically be held liable for negligently transferring control over the assets of his depositors.
From the facts known to me, this seems like an extremely unlikely way for events to turn. It seems, at least to me, that Zhoutong negotiated in good faith, believed the people he were dealing with were more competent than him to run the business, and had no reason to suspect any of the future problems. I don't know whether his compensation was fair or not, but I understand he was motivated to sell, so it's unlikely he was paid more than the business was worth.