He feels old that night in the tower, far older than he has ever felt before. And yet, as he stares death in the face he can't help but think of all the things left he could do, and wonder if he really deserves this.
His first thought, as has long been habit, is for Hogwarts, and the students she protects. He has long since lost track of the number of years he's spent in these halls, first as a teacher, then as Headmaster, but always providing help and guidance wherever it was sought. And once he was gone who would protect the children? He had faith in his staff, of course, but as he looks at Draco and the boy's over-bright eyes, laced with hidden fear, he can't help but think there is still need for him here.
If his first thought is for the safety of Hogwarts, then it comes as no surprise that he should next think of Voldemort and of Tom Riddle. He accepts that he has failed Tom, that there will be no more second chances or attempts to save him. But even if he can't save Tom from Voldemort, there are still others out there that he could. There were people out there dying daily, people he could save. And when he was gone, he would leave the Order of the Phoenix leaderless, and without anyone with the power to face Voldemort.
Except Harry Potter. Harry Potter, a sixteen year old boy left to defeat the most evil and powerful wizard since Grindelwald. He needed to protect Harry, to make it so passing his N.E.W.T.s was the most worrisome thing the boy had to deal with. Instead he would die here and leave Harry the responsibility of taking down Voldemort, all because of a prophecy. He knew there had to be a way around it, a way to keep Harry safe, but he wouldn't live long enough to find it.
Severus approached him, wand in hand, and he couldn't help but think of how he had failed this man too. Failed him as a child and failed him now as he pleaded for death. Severus thought he knew what killing the Headmaster would cost him, but Severus didn't really. He had never told anyone of this plan, so it would appear to the world that Severus really was a Death Eater and the respect that Severus had slowly earned over the years, which Severus valued more than he would ever say or even know, would vanish like the morning mist. Severus had no real friends left, and now he would die and steal all of the other man's acquaintances as well.
As death stalked slowly near he felt his thoughts begin traveling back and back over the well-worn paths in the corners of his mind. Aberforth had never really forgiven him for what had happen all those years ago. It was only fair, as he had never forgiven himself either, but in his last moments he had to consider that there had been something else he could have said, something more he could have done for his brother.
In the end he didn't really have to wonder if he deserved death. If nothing else, the utter look of revulsion on Severus's face told him he didn't. And so it was he had one last thought before he sunk into oblivion. The sorting hat was wrong about me, he muses as he gratefully runs away from the pain he has caused, and the responsibilities left to him and into the abyss to find the loving arms of his long dead family. I've always been a coward.