We know that Guo Jing, Huang Rong and their son, Guo Polu perished when the Mongols' troop finally took down Xiang Yang. According to history, that will be around 10 to 20 years after ROCH. By that time, GJ and HR was almost 70. There was no mentioned of the couple having any grandchildren.
Guo Xiang became a nun and founded E-mei sect, that ruled her out from having any child of her own.
Guo Fu and Yelu Qi had no child by the end of ROCH and we didn't know if they had any offsprings.
Guo Polu was hardly mentioned at all.
Even if they had any child, their descendents would probably stay in Xiang Yang till it was perished. However, the Guos were great heroes in their time and deserved their family line to be carried on.
If I wasn't wrong, XL18Z was almost a forgotten skill in HSDS, perhaps the skill got lost when the Guos perished but could there be a slight chance that someone in the family survived? And if so, where would they be? This is just a random question I have been thinking when I found out GJ and HR died together in Xiang Yang and I hate the idea of good people dying without leaving behind worthy descendants.