On the one hand, I totally get the emotional aspect of where this is going, so I get why ties were cut.
On the other hand, I don't know that the grandfather would maintain the "never show your faces again" position when Millie turns out to be a recipe mill; if he were to insist, there'd be a very good chance he'd lose his position within the guild for failing in his responsibility for looking out for the best interests of the guild. If he were to put his personal feelings ahead of guild business, he'd be quickly ousted.
The fact the parents didn't think of this is really kind of bothersome.