@SydneyCarton
PurpleOkapi That’s an alternative reality novel I’d love to read; what if we’d had King Edward and Queen Wallis? Would they have had an heir of their own or would Bertie have ended up becoming king anyway but years later? Would he still have died so young? Would Margaret have married Peter Townsend if she’d stayed the daughter of the duke of York, and would Elizabeth have become just another navy wife?
I'd totally read that. My guesses:
They never had children, so either they didn't want them or couldn't have them. If the former, Edward's willingness to hand the throne over to George and then Elizabeth suggests that he'd have been happy enough to remain heirless and let them inherit when he died. If the latter, then the probably still wouldn't have been able to have any.
The stresses of being King can't have been good for poor Bertie, but I don't think that's what gave him lung cancer. He'd still have died around the same time.
Elizabeth would have ended up as Queen but not until Edward died. Edward would have been on the throne during the Peter Townshend saga, and I think he'd probably have allowed the marriage.
It would have been unseemly to groom Elizabeth for the throne until Wallis was so old that producing an heir was clearly out of the question, so perhaps she wouldn't have been as well-prepared for it. But on the other hand, she'd have been much older when she became Queen. Mountbatten would probably still have flung Philip at her, but maybe not, and who knows whether she'd have married him? On the one hand, maybe his background would have been less objectionable if her becoming Queen wasn't considered a sure thing. On the other, maybe she only got her way in the end because she was a future Queen.
Also, the allies would have lost WWII and we'd all be speaking German right now. 
This is fun!