I mean, it's possible that they are currently doing all the refactoring and cleanup that has been neglected in previosu years. This would also explain, why they are not able to produce more content at the moment (and why it's so costly). If this is actually the case, then there might be light at the end of the tunnel, i. e. future additions to the game might become less complicated and less likely to produce bugs/regressions.
Also, why would GW3 lead to players abandoning the franchise? This is not what happened with GW2, or did it? I always thought that a lot of former GW1 players are now playing GW2 and some maybe even still play GW1.
My theory is that whatever ArenaNet had in the working during IBS was not good/finished enough or too far off from the current francise that NCSoft pulled the plug and "condemned" ArenaNet to continue releasing content for GW2 (with a much smaller development team on a code base which is increasingly hard to maintain).
I'm not sure whether this is entirely true or rather whether this is true for the more casual MMO player. You are describing the traditional Until Death Do Us Part way of playing MMOs. But GW2's (mostly) lack of vertical progression makes it really easy to return to the game after taking a break or playing something else (another MMO, e. g. GW3), without feeling that you have missed out on a lot.
By the way, this is one of the things I do not like about the new daily system (wizard vault), because it kinda discourages playing something else or taking a break, unless you are able to ...