To say that Genghis Khan was an important influence on the development of Gwok Jing's character is an understatement, but I wonder if one particular concept that the Khan introduced to Gwok Jing early on didn't fully manifest until much later in Gwok's life.
Some of Gwok Jing's critics point out that his decision to sacrifice his younger daughter Gwok Seung (if necessary) to prevent the Mongols from overrunning Seung Yeung Fortress was callous. Gwok Jing did seem prepared to sacrifice even family members if necessary for what he regarded as the greater good.
I wonder if this idea was first instilled in young Gwok Jing by Genghis Khan during the (young Kereit nobleman) Dosi incident. The young Gwok Jing confronted Genghis Khan in the latter's tent after learning of Genghis' intention to betroth Princess Hua Jeng to Dosi to strengthen ties between Genghis' own tribe and the Kereits. Gwok Jing believed the Khan was heartless to sacrifice his own daughter's future for political reasons. After Genghis explained his position to Gwok Jing, however, including the all-important need to unify the Mongolian nation, Gwok Jing relented. While it cannot be said that Gwok Jing completely agreed with Genghis Khan's position at the time, he certainly understood and accepted it.
Perhaps this is why, some forty years later, Gwok Jing was prepared to sacrifice one of his own daughters to prevent the Mongols from overrunning Seung Yeung Fortress. The older Gwok Jing might have recalled the difficult decision that Genghis Khan once made in consideration of the welfare of his own nation.