There is some context to Con's absence:
1. CAG had a 6-man crew:
Steve went on to be a game dev on the mobile platform, and last I heard, Sev went off to college. This puts a significant dent in the capabilities of an already-small dev team (remember, this is one of the most popular browser-based MMOs, yet it only has a 6-man team compared to backyard monsters or other FB MMO/basebuilders).
2. While I have not played actively since 2016, the development potential of the game is limited; there is only so much you can build on the old deadzone code. Flash as a whole is on decline (most Kong/AG games are now coded in HTML5), and Kong is a basically-dead server (chat-wise).
With how old the infrastructure the game is built on (TLS:DZ always had performance/login issues due to the way it was coded, and flash presents its own issues) and how there is a limit to how original that new content can be (right now, it's constantly scaling weapon damage and infected health in tandem with level), it doesn't make sense to continue developing DZ.
3. After Warfare Online shut down on October 31, 2017 due to low playerbase (therefore not enough microtransaction purchases and the resultant revenue), I'm sure no developer wants to see their game die like this, especially since it took 2 years of work to develop (longer than it took for TLS: UC, mind you, which was Con's crown jewel and the pride of the flash gaming era). He might have taken a hiatus from developing. Perhaps a vacation or something to collect thoughts and figure the way forward.
After all the above items happened, and after a long stretch of forum inactivity, I think that we may be on the brink of something new. Deadzone will still roll in revenue, but I imagine the "business" side of things of CAG is getting changed to reflect their current development capabilities (amount of capital available to invest in development) and they are gearing up for something new.
I don't see much for DZ, but I see a bright horizon for a thing such as TLS: UC II. Perhaps we can finally find out what happens after the player leaves Union Island, or what happens to Jack.
I would like to end this by saying that this is just what I have gathered over my time doing TLS and Warfare Online. This is not official, rather it represents my best guess for what is happening based on the information that I know.