Many viewers have a theory that the Night King will not attack Winterfell himself but rather Kings Landing. I think him using his forces as a diversion is a decent tactic being he can easily create more but I don't see him taking on Kings Landing just yet. Assuming he does a dragon aeriel assault then most of the dead will be either buried under rubble or incinerated. Also, can he re-animate while flying overhead or does he need to be in close proximity? He can't get too low cause by now Qyburn should have made more ballistas and maybe catapults. The Golden Company was created by a Targaryen so they may some knowledge on how to battle a dragon (although maybe not a dead one). Of course the obvious reason is with the city destroyed, citizens dead, her armies destroyed, Cersei would be taken off the table in the third episode with three to go. No one wants that.