I'm not really sure what factors people take into account to consider a game dead. I'm guessing for Quake it's a combination of: tournament activity, playerbase compared to other games, playerbase compared to Quake in the past, and quantity of updates. Most people would see all of these factors as being fairly low I'm guessing, so the conclusion is that Quake is dead. imo Quake isn't dying but, like anything, it will eventually, it's only a matter of time (this doesn't only apply to Quake, mind you)

Players not coming in along with players quitting and low population.

As far as the NA scene goes, most people aren't saying the pub scene is dead. It's the competitive side of the game, which is what quake is about. There is a total of 0 competitive teams in NA, combined with no duel cups such as Zotac.

game is dead when u have problems with playing ffa on public server...

inb4 dutra