But I think that will be the final message of the show; power is corrupting. And the only people who are truly good at wielding it are those who do not seek it. But it's not really a happy ending because while it will be good for the land, it will not be good for Jon himself.
Tyrion will like die at the hands of Daenerys or her army. He's my favorite character, but I think he's done for. Game of Thrones never lets the wrongs people do go unpunished. It may take awhile, but they get theirs eventually. And Tyrion will have to answer for his betrayal of Varys. It's sad, because he genuinely believed he was doing the right thing. But at the end of the day, the bottom line is it was the wrong decision. He backed the wrong horse. He was so desperate to believe in Daenerys that he was blinded to her power hungry instincts. Even though he meant well, the show will not let him live happily ever after after that. I do think and hope that they will give him a chance for redemption though. Like maybe he sacrifices himself to save the realm.
Arya Stark will kill Daenerys, fulfilling Melisandre's prophecy. And whatever machinations Varys put into place before his execution, they will ensure that Jon Snow's rightful claim to the throne is honored.
It will not be a happily ever after ending. But it won't be all bad either. That's my prediction.