I see a lot more benders in Don's future, how 'bout you? (spoilers)
The dropping of the cigarette into the glass of whiskey is symbolic but it doesn't really mean anything. The big Hollywood rapprochement with Helen, that doesn't cure alcoholism, the idea that he's going to crank out one great book and be magically purified is just as ludicrous.
There's really nothing to suggest that five minutes after the camera is gone he's lost his confidence again and he's tearing the place apart looking for another hidden bottle. In my opinion Bim is right on when he pegs Don as the sort of guy who'll be back time after time.
I think Wilder beat the system and produced a "happy ending" with plenty of room for doubt.
Opinions?
It feels like an Arby's night.