Well, telling someone going to a serious surgery that they'll die will make them feel like they will, which will lessen the chances of successful surgery (due to body having already given up), so you could argue that he is partly responsible for her death (assuming she did die). Then again, he is a kid, so he most likely wasn't aware of the implications (kinda like how real kids wouldn't be, either), so he can't really be blamed for it, especially since based on how he's speaking about it now, it seems like he has realized what he did and is regretting it.
Doesn't change the fact he has been a cunt in this story so far though.