Your right, if the house of Valois-Burgundy manages to survive that long. If not, this kingdom would have been inherited through the female line; which was one of the requests import to the Burgundian dukes during the negotiations for a crown and the practice in most of their holdings. The duchy of Burgundy is a 'special case' though, historically the Capetian dukes of Burgundy had that privilege and that was claimed by the Valois dukes of Burgundy too, however the king of France tended to see Burgundy as an appanage. This partly has to do with how king John the Good inherited Burgundy and that he stayed king of France and duke of Burgundy and thus keeping Burgundy separate from the French crown. He later left Burgundy to his youngest son and that grant was confirmed by his successor (and eldest brother of the new duke of Burgundy).
Depending on the time of such a succession, a coalition could have forced to leave this kingdom to a younger son, when they inherit France. OTOH
merging those will probably face similar difficulties as IOTL England and Scotland, before Great Britain and have similar issues afterward. Certainly if it was independent long enough and managed to stay relatively intact.