I've found the information I was asking for. It proves that I was completely wrong, so my apologies:

Reassessing the Merger of FFXIV Worlds (02/12/2012)
Quote Originally Posted by Naoki_Yoshida View Post
It’s hard to explain, but if you want to keep your character on the World you are currently on, then you don’t need to do anything (if there happens to be duplicate character names, we will ask you to make changes however). You needn’t worry as you are not going to get kicked out from the World automatically or be forced to move.
I'll be editing previous post (not deleting...) in order to emphasize the fact that it is wrong information.

Quote Originally Posted by Timotheus View Post
Is that really necessary to design everything at THIS level of foolproof?
There's no need to be that rude. I was just asking for help and not insulting anyone.