And I liked Don. But he was never better than after he dumped his ad man life. Going back to it is a fate worse than death.
Of course he will ultimately fittingly die of cancer, just as he suffers for his wife at the hands of ad men like himself (they sold and still sell nicotine, yo). No ad men. No smoking. No cancer. And that's what Hollywood is all about. Happy endings at any cost. It makes the execs happy.
But ironically in this case, it exposes the reality of 70's hype that killed what the sixties stood for. And that is why it’s a great ending. It is truth. It is exactly what happens and what did happen. And you call that upbeat? Get cancer and see how upbeat it is.