When the war ended, McGonagall put up portraits of all those who died fighting Voldemort in the Battle of Hogwarts.
Harry ended convincing her to put up a portrait of Snape. When Albus Potter went to Hogwarts, he and Snape both loved talking to each other as they were both seen as oddballs- Albus because he was a Potter that went into Slytherin, and Snape because nobody ever really accepted him except for Lily.