Gmod dead?

Oh boy, you can be sure that GMod is not dead. Sure communities rise and fall but that's normal. No community can hold a decade of playing the same game/gamemode over and over again.

Take MesaGaming as an example. They ahve been around since 2015 and had a great playerbase throughout these years. However people probably got bored and MRP eventually died and now they are creating a DarkRP server which looks really nice imo.
IceFuse has also been around for a while now and it's actually being able to maintain it's popularity. I would say that's because of the variety of servers they have.