The idea of Lupin committing suicide frightened me, and I'm not sure he'd do it necessarily, but it worked for the story. I enjoyed reading this.
The idea stemmed from some discussions that I had with people at Sectus immediately after DH came out. There was a lot of joking that perhaps Lupin had faked his own death to get out of his bad situation -- since he couldn't seem to grow a pair and get out any other way. My brain sort of took the next logical step. Lupin's a survivor, really, and so I don't think he'd be the sort to commit suicide in a premeditated fashion. But in a situation such as a battle, where there was a split-second decision to be made, and where he suddenly saw an opportunity out... I think it could happen. After a lifetime of pleasing other people, he doesn't seen to know how to stop, and that could certainly create the right sense of desperation.
Yeah, Lupin and Snape are really more alike than either would probably be willing to admit. Heh.