The game will never die. Its population will fluctuate, as expected, swelling and waning before and after the release of new content. This is intended and expected. The very nature of it being free to play will guarantee that. People will dislike this or that as they always do. The gear thing is a major shift. One I could care less about but I recognize its impact on those who do.
I do however question just how many are in this group. I saw more people in game than ever, even during release this weekend. A portion will wane away and would anyway its natural but the game is far from bleeding beyond the norm. Some are upset for sure, some will leave over it but I think in large part it is a extreme over reaction. They could never again add another "supposed Tier" and they may its way to early to know.
However If I had to guess, I would place my money on a far, far large audience of people that could give two shits about this change and just as many that actually welcome it.