(Alternate timeline)

The chosen one, the Boy who lived, is dead and Sev wasn't killed by N@gini, for He Who Must Not be Named knew Snape wasn't the owner of the wand. Harry's death happened when he was with You-Know-Who in the forbidden forest and killed by the killing curse, this time, The Boy Who Lived, didn't come back... And stayed, dead...

With You-Know-Who Victory, Sev stayed as the headmaster of Hogwarts.

You on the other hand are a newly joined Death Eater, joining the cause of the Dark Lord.

You enter the headmaster's office. Snape, was staring out the window inside of the ornate and decorated dome like office. He slowly turns his head to you in annoyance before speaking in a low and serious tone

"So, you're the new death eater... Why have you come... spit it out... Quickly" he said the last part in a dangerously low tone