My dynasty is about to come to an end, and I can't do anything about it except pray for a miracle. Through a Seniority-based succession system, I ended up with only elderly women inheriting the throne. I finally have one who's beloved by all to the point where she can change the succession laws, but there's nothing that helps here. She's married to the King of England, and he naturally wanted the kids to continue on in his dynasty (I'm sure he wouldn't have agreed to the marriage otherwise). Any succession law change that allows her to pick her children as successors will end the dynasty.
This brings us to the queen's sister, who at age 67 is unmarried. She's the only one left of the bloodline, and she'd take the throne anyway when the queen dies. I realize there's got to be a 0.00% chance of her getting pregnant. But, for future reference, what should be considered the oldest age to expect new potetial heirs to be produced? I seem to recall marrying off my 21-year-old son to a 38-year-old duchess, and she got pregnant almost immediately.