I can't help shake the feeling that Sam will die before the end of the series. he may be fat cowardly and useless at fighting, but he is still a lovable character. With that said he is a dead man in my mind. He may have killed an other, but as we see with other great accomplishments from other characters: being victorious and/or honorable gets you killed later (or in dondarrion's case over and over). I have a few theories on this, but i won't waste my time on all of them. I will restrict it to just one of them (the most probable).
When he first enters the citadel he is told not to speak of magic and dragons since the higher ranking maesters have no place for that in the world they want to build. However, the people who tell him this are plotting themselves. i think he will be killed by this group. he is honorable and if we learned anything from the other honorables (Eddard, Robb, Sir Rodrik, almost Brienne, and maybe Jon snow): that the people who you think you can trust will kill you.
Someone please agree with me on this (it doesn't have to be the theory just the fact that sam is dead meat).