The way 343 is handling things now has halted the decline of the series. They are doing an excellent job reminding the existing fans why they love Halo by elevating the MCC's value and making it even more accessible. From what I've seen, this has decreased the negativity in the hardcore community a lot. This is probably being done to prime us for the release of Infinite, but it's still great for the fanbase. I think true revival for the series will depend on the quality of Halo: Infinite. I think if they can get that game off the ground successfully, the series will branch out and it will become a far more relevant franchise like it used to be, similar to how the new God of War game did for that franchise.
Is Halo making a comeback?