I mean, if it’s a one time payment then he has no reasons to regret the decision even if the users dropped off. On the other hand, if he was expecting a recurring royalty from the buyer, then he didn’t think it through.
PS: I’m not justifying his actions in any manner. If a sale without a heads up is deceptive, his last reply was outright indignation. I’m just trying to understand whether he actually regretted it or not.