If you have any of the information used to create the account, an SE representative can get it back for you pretty easily.
This thread tells you how to contact them: http://ffxi.allakhazam.com/forum.html?forum=10&mid=1259779523309379427
Did you create a Square Enix account before you quit? I think there's even an automated password recovery function in there.
It is definitely worth returning, and the economy is a bit inflated overall, but that just means a lot of money is being thrown between HNMs for the most part. Last Saturday I seriously got down to it and made a million gil in one steady afternoon and evening, but there was a good bit of luck and hard work involved in that. Edited, Feb 14th 2013 10:20pm by catwho