Does a spell hit a target thats been flickers?

alright seems obvious that it fizzles but hear me out.

this involves a tutor line in my [[mairsil, the pretender]] deck:

I have Mairsil in play, he has [[endling]] and [[Kagemaro, First to Suffer]] in exile with counters.

i activate endling to give mairsil Undying, I activate Kagemaro, sacrificing mairsil, I have 5 cards in hand, so all creatures get -5/-5 till the end of the turn. does this mean mairsil dies for good? or does he avoid it with undying?

second question, if mairsil has deathtouch when I a ping-all-creatures ability that requires sacrificing mairsil to cast it, will they all die? if not, how about if she comes back with persist