I think Zombie apocalypse would make things interesting - but that could be just me.
How about just general Post-War future, where the Purist have tried to take over but failed - though just barely.
Loss is at either sides. So yay for killing characters!
All the remaining Purist are gathered and locked up. And it's basically just people trying to pick up the pieces. So lots of potential for drama muse.
But - people are sick and tired of Purebloods trying to take the world over so there is an Inquisition after any Pureblood family.
The ministry confiscates the estates of any Pureblood in question. There's a real big stigma at being a Pureblood - so basically it sucks to be one.
We can have lossa fun with this - arranged marriages, purebloods beig poor and Purebloods just generally being pro-muggles the works! XD