WI: Edward II Remains at Caerphilly During His Flight?

During his long, pathetic retreat from the invasion of Mortimer and Isabella in 1326, Edward II and his retainers fled to the very strong defensive position of Caerphilly Castle. He abandoned it (along with much of his cash and other valuables) in early November in a probable attempt to flee abroad, and was captured during a futile return to it. Almost every historian rates his leaving of Caerphilly as a poor tactical decision within the broader strategic disaster that was the reign of Edward of Carnarvon, saying that he could have held the castle for a long time even against an army. But, if he had stayed and attempted to fortify it, would it have changed anything? Would he have been able to extract terms from the invading clique and had enough power to ensure that he avoided his OTL fate? Or was the broader situation just too far against him?
 
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