Basically, you need to constantly moderate the game and reports to lower hackers fully, create more fun clan tournaments and proper events and basically make the game enjoyable for everyone from questers to clan wars. And stop trying to add new stuff into the game like that Blitz crap it's like quest and clan war mode for sprayers.
Basically, keep on top of hackers. Have daily events and monthly tournaments to make it competitive in clan war. This will most likely bring many people back into gunz and try if possible to implement Anti-Lead into Aeria as most people have moved to private servers which have this feature and clan war a lot which have taken majority of your players away.
If you want to keep this game alive and fun and most importantly to give you guys a good reputation I'd recommend my suggestion however the rest is up to you.