I recall last time I quit simply reading through the story history was more than enough to refresh my memory. Actually, if I remember right you can even replay some of that content as there was "hard mode" achievements or something around some of it.
Downloading the game after being gone a while as well... thought I heard ArenaNet was shutting down or pulling resources from GW2, then I hear they're planning another xpac, cool :)
For me, I know I completed up to all the xpac Path of Fire stuff, but any story that has come out since then is going to be new to me