I wonder if he ever considered allowing Olga to inherit if Alexei died without heirs? Surely the family considered the possibility that Alexei would die young and therefore changing the laws of succession may have made the family breathe a little easier. But then, knowing that the crown may possibly go to Alexei might have made Nicholas try harder to conceal the truth and protect the throne for his son, no matter how misguided it was to conceal the truth about the heir's health.
Impossible. The tradition of the throne passing only to males was very strong and there were plenty of males available.