The Losers managed to defeat IT at the end of Stephen King's IT novel, but clues in some of the author's other books suggest that Pennywise may actually still be alive. King’s horror novel IT was published in 1986, and although it was first met with mixed reactions, it is now considered one of his best works. The novel has been famously adapted into a miniseries in 1990 with Tim Curry as Pennywise, the Dancing Clown, and most recently in a two-part film directed by Andrés Muschietti, which concluded with IT Chapter Two.
IT follows a group of seven children self-named “The Losers Club” living in Derry, Maine, who are terrorized by an evil, shape-shifting entity living in the sewers. This creature uses its ability to take the shape of their greatest fears and phobias, although its preferred form is that of Pennywise. The Losers finally defeated IT 27 years after their initial encounter, but what if it somehow survived and is still present in Derry’s sewers?
A Reddit user noted a couple of hints in other Stephen King stories set in or around Derry that point at IT still being alive. The first one is in The Tommyknockers, a sci-fi novel published in 1987 in which the residents of Haven, Maine, start falling under the influence of an object buried in the woods. In this novel, the appearance of a clown in a storm drain is mentioned at some point - Pennywise attacked Georgie Denbrough through a storm drain in IT. Another reference can be found in the 1994 novel Insomnia (which is set in Derry), where it’s briefly mentioned that Ralph Roberts sees an “aura” coming from the storm drain. In Dreamcatcher, another story set in Derry, there’s a statue with a graffiti that says “Pennywise Lives”.
During the Losers’ final battle against IT, Bill destroyed IT’s heart while Ben destroyed the eggs laid by IT, as its final form was that of a giant spider. But as other Reddit users pointed out, Ben wasn’t entirely sure he destroyed all of IT’s offsprings, so it could be very possible that at least one of them is still alive and living in the sewers of Derry, having also survived the collapse of the downtown area. Others have suggested those sightings are just impressions left by IT’s death, while some believe it was just a bit of fan service from Stephen King. Considering how many references King makes to his other works in his novels, that's certainly a possibility.
Whether IT and, therefore, Pennywise is still alive and roaming the sewers, not only in Derry but in its surroundings, too, or King was just having fun with the character, these hints certainly leave the door open for him to revisit the character in the future, if he decides to. Until then, King might continue to drop some references to the famous killer clown in future works – after all, Stephen King’s universe is a connected one, too.