CSGO might be going down in active users, but not dying, not yet at least.
Personally I think Valve have scared off the more loyal users and are just getting more kids into the game, they made it free-to-play which got rid of a lot of members and brought a ton of hackers, there are steam account makers, more cheats and there are more ways of exploiting the system now.
But I think they had their reasons for making it free-to-play, one I think that might be true is that they want to make VAC better, and allowing cheaters come and just play for free for them to monitor it and upgrade their system would of been a good idea