In my opinion, Call of Duty will not die until the Xbox and PlayStation die. As far as I am concerned there will be no new system coming out that isn't a PlayStation or Xbox. If Advanced Warfare comes out strong, then there will be at least one more game. Depending on the statistics of pre-ordering and people still playing Ghosts, at least one more game has to come out. There are some bad statistics with Ghosts though (Those will be in another paragraph or two). With the Xbox One and PlayStation 4 coming out, and Microsoft promising at least one more console, Call of Duty will have at least 2 more series, with Call of Duty Advanced Warfare and hopefully another series from Treyarch, the creator of Black Ops 1 and Black Ops 2.
Call of Duty: Ghosts had record low launch sales which had many concerned, but still beat VGChartz predictions of total sales. It's clear that console consolidation killed the next gen versions population in particular the Xbox One fanbase. Ghost is still the top selling next gen game with 2.2 million copies on PS4. Ghosts has sold a total of 21.3 million, and when people move to next gen I imagine it will gain a couple million more. The entire industry is selling less games. Battlefield 4 has sold just 9.6 million copies, and peaking at 2.9 million on Xbox 360. Titanfall sold 2.76 across its three platforms which includes bundles with the Xbox One. You can bank on the fact that Ghosts was still extremely profitable for Activision.
Online population is low, but it's not as low as people think because BO2 population statistic has always been off: Ghosts sold about 8 million copies on Xbox 360 so I will use comparisons. Halo 4 had about 8 million sales after six months, too. Halo 4's online population after six months would only hit 30k on weekends at its peak. Even early in the morning Ghosts has more players than Halo 4 did at its peak, a game that sold the same amount of copies. The game is still one of the top 5 most played games on Xbox Live without a doubt. Microsoft has been reluctant to release the live chart, but some people commented it's because people were bashing Gears of War Judgement and Halo 4. Ghosts is not the most successful COD, but it's far from dead. With all the negative hype for recent CODs you would expect it to be much more dead. Halo 4 was critically received from reviewers, but the online population died.
In comparison to recent CODs I personally think Ghosts is a huge improvement. I enjoy Ghosts maps because there is a variety. I prefer the freedom of choosing what weapons I use when I want instead of being forced to use certain weapons at low levels. I use more weapons in the new unlock system because more are viable and Ghosts has good balancing. I detest the idea of moving back to a strict unlock system, and frankly I never prestiged due to it. Also, I like the perk system in Ghosts because it allows for a variety of playstyles to shine. Snipers and Shotguns are actually balanced for once...granted if you watch certain YouTubers they will still call them overpowered (402thunder402), but those people are not being reasonable. Your complaints are opinion as is my praise.