According to Activision's CEO Eric Hirschberg, Bungie is already working on future DLC's for Destiny (beyond "The Dark Below" expansion and "The House of Wolves") as well as the "next full game release." So, it looks as though all of us who really enjoy Destiny can expect Destiny 2. According to reports Destiny currently has around 9.5 million registered users who average 3+ hours of gametime every single day, so it's no surprise that we should expect another Destiny title with that kind of success. Destiny sold more than $325 million in games in it's first 5 days, which makes it the largest launch in all-time gaming history for a brand new IP, and ranks within the top 10 among all time game launches.
No reports yet when we should expect Destiny 2, but we imagine that it will probably come within the next 10 years, as that's how long Bungie's publishing contract with Activision was set for. Bungie says that they have a story to tell with Destiny that they plan on releasing over the next 10 years, and that story will obviously continue in future expansion packs and now it seems, Destiny 2.