Is Gmod dying

I don't think that's possible, there are still a lot of private servers still active.
Facepunch does not have a public server, it does not lose money and win with sales.
Imagine closing 3000 private servers overnight. For me it's not possible.

There arent as much players as before few years but dont think it will die so easily.

I have heard countless of people say GMOD is dying but it doesn't seem so. DarkRP and all the other game mode seem to be holding up well but yes, some other game modes are slowly going down the drain.

the old community Garry's mod begins to leave the game, but it is normal as old will go, and new ones will come

I think not, there is lots of servers and players. But maybe one day we will get Gmod 2

GMod is reaching those days, but as Soulkest said, there is plenty of players and servers up still.

I don't think so, look at the playercount on darkrp and sandbox...

it wouldn't die if fortnite never existed and other battle royale games

I do not think that Gmod will lose its online, because it has become popular among youtubers who have their servers there.