Well, I do remember that we mailed quite a few people a while back who hadn't been active for well over a year to respond or have their account swept up with a clean-up...but a year+ is more than enough time to come back if you find you have time.
I'd imagine your account will stay around after you leave in the event that you want to stop by and check up on things. When people leave, they generally say their good-byes and go on, but if you are ABSOLUTELY positive that you are never going to return (which can't really be told at this point in time, you never know when your interests will shift), then I suppose a deletion can be arranged, though it seems a bit hastey....