If you did deactivate your account properly (go to contents and deactivate them during a billing cycle) the system will "park" your account and nothing happens. Originally (and this is what is written on the original documentation for this game) contents would be deleted after three months of inactivity. You would be able to use the FFXI code again to reactivate the game but would need to start the character from scratch.

Then sometime in 2004 they changed it to how it is now: You can deactivate and it will be left alone.

Now if you have invalid billing information and SE tried to charge you, you canceled the *whole* account (there was an option for that on the old Service and Support page for POL) then there is an countdown of three months before the account is completely removed.

After the account is deleted and removed from the database it's impossible to log in it through POL Viewer. And that's what this server is meant for.