Sanae becomes the new Hakurei and much despair all over Gensokyo
Sanae fueled by despair and anger become stronger, overthrow Suwako and Kanako and with the power of Miracles saves Reimu and makes a new Gensokyo barrier.
Then she marries Reimu, unify the shrines and have lots of Miracle babies.
The only tragedy here is the writing: the plot points don't even have time to breath, let alone develop properly. I'm not even sure what the hell happened at the end, other than the author going full 4edgy6you.