If they were to implement a system to "delete" characters, I would imagine that it would simply be moving that character to "deep storage" and would require the player to do a process on the website in order to bring them back out. Additionally, this process would require the player to "rename" their character because they would have been literally placed outside of the server storage space and would mean the separation from any housing, Free Companies, and mail they might have had previously. This of course would only apply to characters that were below the maximum level at the time they stopped playing, and would probably require the player to be out for at least a year.