Cancel subscription

Q u o t e:
When you cancel subscription, your payment information is removed from the databases. That means that no one can renew a subscription with your stored credit card. It also cancels any recurring payments (obviously).

You still have whatever game time you've paid for left to play (all game time is prepaid).

Should you let your subscription lapse completely, your account will become "frozen". All this means is that you won't be able to log into it. Your characters will still be there, with all of their things, waiting for you to renew your subscription - which you can do at any time.

***Quoted for Turtle***

The above is spot on, Supapally! The only changes you should bear witness to are changes that are made to the entire game, via patches and updates. The only other change you may notice is the expiration of any Auctions you leave running while your game time lapses, as well as items in your mailbox expiring.

Other than those slight changes, you should be able to return, at any time, and pickup where you left off.