OK, let's leave aside PvP, WvW, explorable modes, achievements, secrets, confirmed post-release content patches and expansions. Let's assume ALL those don't exist.
And once a person has done this?
Well, then you move to another game, and realize you got hundreds or thousands of hours from a game that costs 44$. Did people ask what did you do once you finished Dark Souls, if you didn't want to play New Game Plus or PvP? Did people ask the same of Mass Effect? Of Arkham City? Did anyone seriously contend that these games sucked because there was nothing more to do once you had done everything (even though "everything" is orders of magnitude more in GW2)?
No? Then why is it an issue here? Seriously, at what point did we let game publishers convince us that a game must keep us hooked for the rest of eternity for it to be any good? At what point have games become supposed to continue after they are over? For me, if I get a great experience out of a game for enough time (certainly more than any other game of its price point), what more could I want?
OK, I think this is, yet again, linked to the same issue of "I'm not enjoying Guild Wars 2; I just want to get to level 80 so the game can start". If you're not enjoying GW2 as much or more than any other (even single player) game, then frankly, you should not be playing it! I don't mean there's anything wrong with you, at all; I'm just stating the obvious that you should not play a game you don't enjoy. No, really. At some point MMOs managed to mess up the most basic, obvious laws of gaming.
What's more, GW2 won't change (it's STATED not to change) at level cap, so if you're not enjoying yourself on the way to level 80, you will not suddenly find an amazing game waiting for you at that level.
Sorry if it seems like I'm ranting, it's just that I don't understand what's wrong with a game that's good in itself, and then ends (even if it's not necessarily the case here). You just treasure the memories, play whenever you want (for any of the content mentioned at the top that you enjoy) and wait for the next expansion. And you're not a dime poorer in the meantime.