I kind of have a feeling that the reason Snape took on stuff like the unbreakable vow was not just because he wanted to do good in his very difficult way and because he had compassion for women and children on some level and because he didn't fear death. I have the distinct notion that the hand he extended for the unbreakable vow was also a hand he took. Not consciously I think but certainly subconsciously. It was the hand of a woman who offered him a way out, who offered him a way to die. I'm pretty sure that he wouldn't have killed himself because he would consider this weakness and he seems to despise weakness deeply. He also didn't want to die in a useless way I would think, just dying of a random illness or something was probably not his first choice even though I think it's not far fetched that he had suicidal tendencies since his childhood and who could blame him, there wasn't much love in his life ever.
But dying for a good cause, something he himself considers good and worthy, now that's another thing. I think he loved his mother and I think he had a comparatively good relationship with her even though it probably wasn't that close. But seeing this theme reappear in his life I would just dare to make that claim.
And I think he really couldn't deal with his big negative feelings and there was so much hopelessness, so I think dying a hero was, from his standpoint, really the best way out.
