1. Snape survived Nagini and the Trio become his protectors while he's still very ill. They take him to Grimmauld Place to recover. Turn the cliche on its head - Snape makes friends with Hermione (who is his intellectual equal) and Ron (they both love Wizards' chess and are evenly matched) and Harry gets to understand Snape better by watching him interact with his best friends. 2. Snape survived Nagini but the Wizarding World wants him killed/imprisoned/tried for Dumbledore's murder. All except the Weasleys, who, much to his alarm, adopt him while he is recovering. Ginny & Harry broke up amicably so Harry is still an honourary Weasley as well. 3. Snape, Harry and Teddy, the toddler Metamorphmagus and chaos-inducer, meet by accident after the war. Teddy isn't fooled by Glamours and imitates the real Snape under the disguise.