Alexander III, king of Scots died suddenly and without children during a nocturnal ride to go visit his new wife. His three children from his first wife Margaret Plantagenet of England had all predeceased him and the Scots estates decided on his granddaughter - the Maid of Norway - as the new ruler of Scotland (don't know enough about Scots medieval history to know if they would've accepted a queen, the English had rejected Matilda as queen regnant a century before).
What if, his son, Alasdair(Alexander) prince of Scots, had survived whatever killed him or at least fathered a child (preferably a son) by his wife, Marguerite, daughter of the comte de Flandres before politely dying?