Does it have longevity? Yes, like many people have said, it you does not burn yourself out, i have seen it way to many times, like my m8 in wow, he comes back to wow, play 24/7 for 4 weeks, then after that he stops. Guild wars is a fun game, but guild wars " road" is what the game is about, Guild wars do not have end game contenst, many people have said it, PVE is just stupid " oh we have no tank or healer" yeah, a wipe party is fun... But the PVP is amazing, and the world also just feels fun, as an engineer it never stops being funny running around with a flame trower, and then 10 mins later haveing greandes, or a elixir gun.
It is a game that can be played for a long long time, it has the most fun PVP there is, the world is fun, you can not outlevel contenst. But NO it will never have as many players as wow does, or did. If you over play it, you will get sick of it, so then it is a no. But i mean i am suprsied that they updates the lost shores for free, that is really big of them, and if they have alteast the major events, it will have a bright future