Who becomes headmaster after Snape dies?

After Snape dies, Minerva McGonagall becomes Headmistress of Hogwarts. This is stated in the epilogue of "Harry Potter and the Deathly Hallows," where we see Harry, Ron, and Ginny dropping their children off at Hogwarts for their first year. McGonagall is seen greeting the students and overseeing the Sorting Ceremony.