Is he legally obligated to follow the shows ending or major plot points? I get that he sent the producers his outline for how it was all to end in his head probably without really thinking it properly through and if he was actually writing it out he probably would've changed it significantly through that process so now he's trapped, he's seen how his rough notes played out in the field and no doubt doesn't like it but if he can't course correct drastically what can he do other than simply drag it out till the end of time, I reckon HBO have him over a barrel