bending the knee would be giving up the north to the dead
danerys (AMAZINGLY CORRECTLY) assumes that he is talking garbage, since dead men don't walk. of course, he actually isn't, so... i guess she's wrong again
the north knows at least somewhat of what is happening, and would rebel against the warden of the north, the bastard, jon snow, who gave up their safety for his life -- by going to bend the knee and live (this is a targ he's dealing with, and they burn people) he would condemn them all to die. this is because he would be forced to call the banners against cersei.
danerys would assume he is bending the knee because he is weak and she has dragons and he pissed his pants at dragons
jon snow is terrible and in the books i think he will end up more like gothBran, because jon snow isn't jon snow anymore, he's unJon. jon is left warged into ghost, dying for his dumbass ideas of forsaking the nights watch. traitor deserved to get knifed, especially because he was dumb enough to believe the words of Mance f**k Raydar pretending to be Ramsay in the pink letter
the show of course has none of these plots ans schemes. in the show the letter is written by ramsay. sigh