Joan is the Queen of Navarre, I think Edward III could have married her instead of Philippa, I think the only way that the Plantagenets can have their Fiefs is that the Fiefs not having personal union with France, a separate line rules the fiefs instead.
I think you mean "the fiefs not having personal union with
England."
If this marriage had occurred, then I think the ruling elites of France would have invented a trick to have someone else than her be recognized as number one in the line of succession to the french royal crown.
All this was not about law or custom. It was about realpolitiks. Law or custom, in such cases, is nothing but a veil that is adapted or twisted in order to legitimize the political solution that the ruling elite wants to implement.
The point was that, by 1328, the Plantagenets had demonstrated for 2 centuries to the rest of the french nobility that their goal was to dismantle the kingdom of France if they could in order to have a constellation of sovereign Plantagenet principalities.
So, it was not possible for them to gain significant support to be chosen as king of France.
The compromise would always favour some insider if the Capetian lineage or of some other lineage whose main fiefs were in the kingdom of France and who was tightly allied to the Capetians.
About the marriage you mentioned, Joan of Navarre did OTL marry Philip of Evreux, that is a Capetian line of the third line coming from Philip III of France (who had 3 sons who lived into adulthood and had male descendants : Philip IV of France, Charles of Valois and Louis of Evreux).
And this marriage was concluded purposedly. Joan of Navarre did not choose her husband. It was concluded when Joan was only 10. And the one who was most influential in this decision was of course her uncle king Philip V of France.
One of the goals of such a marriage was of course to secure that no one outside the Capetian male branches could become a claimant to the succession to the french royal throne.
The so called Salic Law was but the formal ex-post attempt to legally legitimize this political will : no king of a rival foreign great power will ever be chosen as king of France, even not through the hasards and trick of marriage.
They probably became even more uncompromising on this position when Philip II Augustus turned France and its king into the most powerful kingdoms of Europe.
The kings of England, Castile, even less the holy roman emperor, could never ever be freely chosen as king of France.
But I think that the french elites would have had no problem having the king of a small country, parent of the Capetians, become king of France because they considered that this new dynast would have very quickly made France the center of its interests.
This happened OTL with the Capetian Bourbons who were nominal kings of Navarre.
If all the Capetian male lines had gone extinct, this could have happened with other other dynasty's that would have been linked to the Capetians through female lines, in the goal of preventing that a foreign rival great power takeover France through marriage.
