Guess im one of the few who had Kennys back throughout the game... he was all
on seeing me drop Ben and even after showing him the bit on my arm on asking for help he said along the lines of "of course ill come help, youve always been a friend to me". Almost everyone ive seen online had to prompt him with the "clem is family" dialogue option.
As for Vernon and why he buggered off... he was climbing out of the windo and asked "you guys didnt come here by the railroads by chance did you". Most speculate he saw the approaching horde and as such took his friends and scarpered but personally as this should not have effected him in the hidey hole they had i think he instead saw a big ass fire spreading towards them which was initially caused by Lee dropping the blow torch gas tank to try and burn the zombie horde... after all you can hide from zombies underground but there is no escaping mass fire.