Ferenbach published 'This Kind of War' in 1963. The research was done when many of the participants were still in uniform.
Withdraw to the south and trade space for time against the CCF, presumably.
There's a pretty obvious place to draw a defensive line between Anju in the west and Hungnam in the east; failing that, there's another obvious line from Nampo in the west up to Pyongyng, east along the Namgang River, and east to Wonsan.
https://legacy.lib.utexas.edu/maps/middle_east_and_asia/korea_north_rel_2005.pdf ....
The second part of this is is the recognition the Chinese can move through the hills and mountains enmass. The heavily mechanized and road bound US Army was in November/December badly infiltrated and tactically flanked across the board by ridge running Chinese infantry. One of the changes Ridgeway made was forcing the Army battalions up onto the high ground, into the hills & fighting the Chinese efforts to infiltrate via the ridge and dominate the roads in the valleys.
A defense line as described above may not work if the US Army continues to try to 'control the communications routes' in the valleys & leaves itself still exposed to tactical flank attacks from the mountains.
A third factor is if the Chinese Army can move south fast enough and have the logistics support to attack this defense line in december or January. When Ridgeway took over he discovered the UN force had retreated so fast they had lost contact with the main Chinese army. Only the enemy reconissance had been able to pursue in contact & Ridgeway found the US Army was not really fighting much of anyone at that moment. If the Chinese require a extra eight weeks to reach this proposed Anjiu-Hungnam defense line it alters the entire dynamic.
A fourth factor is if the death of Walker is butterflied away. With the UN forces not suffering a December defeat far to the north Walkers reputation is yet intact and there is no immediate or pressing reason to replace him.