Assume all the same members of the royal family, with the same dates of birth and death. (And also assume that there was a way around the whole Wallace Simpson mess)
If King Edward VIII had reigned until his death in 1972, with no children (and his brother Albert (aka George VI) had died in 1952…who would have succeeded him? Who would be on the throne now?
As I understand it, if Edward VIII had died on the throne without issue, with his brother Albert having already deceased, then the next in line of succession would have been Albert’s eldest child.
I.e. Elizabeth.
He had no children, so his brother’s daughter would be the next in line, aka Queen Liz II. Just a little later.
Elizabeth II, who is just another average-length-reign monarch, albeit the longest ever lived.
I believe it would be Elizabeth. The line of succession prior to George’s death would have been George, then Elizabeth; upon George’s death Elizabeth would have become the heir apparent.
Heir presumptive, one should think; in this alternate timeline, it would certainly have been possible for Edward VIII to produce an heir during the 20 years between his brother’s death and his own, who would have displaced Elizabeth in the order of succession.
A related question; who would have held the title “Prince of Wales” during a lengthy and childless reign by Edward VIII, or would it have remained vacant?
Elizabeth. It’s the same line of succession regardless of the actual abdication or death in 1972, in your scenario.
Was there any chance of Elizabeth being next in the line of succession after Edward VIII’s death, had he not abdicated?
With no heir apparent it would be left vacant, as happened in the case of George VI’s reign, as he had no sons.
It would have been vacant. The title is not automatic and it’s not inherited - it’s bestowed by the sovereign onto the immediate male heir. Charles was made Prince of Wales when he was ten.
If there is a female heir, they still enjoy access to the revenues of the Duchy of Cornwall.
Well, that turned out to be a less-interesting exercise than I’d hoped. 
Though since the Perth Agreement if the monarch’s eldest child & heir is female she may be created Princess of Wales in her own right.
Although Elizabeth would never have been Princess Royal, because her aunt Princess Mary, daughter of George V, held that title until her death in 1965.
With Elizabeth II’s reign beginning in 1972, she’s in the top ten of all British monarchs, including Scottish and Welsh when they were separate. Fourth in the U.K., and fourth in England. For the latter, she would pass Elizabeth I sometime next year. I’m not certain I would call that average.
I hate it when that happens.
Hey, at least you get some posts. Sometimes I OP what I think will set SD on fire, and get bupkus.
The evil Wallis Simpson would never let power slip away with her husband’s last breath. Enlisting the aid of Dr. Mengele, a mutant princeling would have emerged from her womb. To ensure the succession of this vile homunculus, poor Princess Elizabeth would forever be remembered in guarded shields as gut Woman in the Iron Mask, while young Princess Margaret would be offered as the prepubescent puppet empress-consort of Manchuko.
She would never have been Princess Royal for a more basic reason; the title is only conferred on the eldest child of the reigning monarch, and in this alternative history she would never have been that.
In real life she was that, of course, from 1936 to 1952, but the title was not conferred upon her for the reason you point out.
That’s true, good point, UDS.
Yes, short answer, your heirs don’t lose their place in line just because you die before inheriting the crown.
Hmmm…tell that to Arthur of Brittany ;).