Prediction: Snape will end up playing a crucial role in the climax of the story, similar to canon but even more satisfying. Evidence:

1. I forget where, but at some point Dumbledore tells Harry that Snape is one of his most valuable allies.
2. The most Snape-centric chapter is called "sunk costs." Notice that this is the name of a fallacy. Snape thinks his life is an unfixable wreck, but he is wrong, and good story telling demands that this be revealed in a suitably moving fashion.