In fact, I just started playing TTT again with some friends. I just set up a new server. The modding community seems to be surprisingly active. Especially regarding TTT2.
As, I put something on someone elses post. i Don't think GMOD as a whole is dead, it is more or less the DarkRP servers that are similar in play style.
I think Garry's mod will last a long time. Modders are still active, they make a lot of assets, the servers are still full of players, I often play with my friends myself
I don't think so, despite the fact that many servers are created over time, creating videos and addons that attract the eyes of players and that invent every new thing