For starters, the big day is August 7th. American PvE servers Set and Wiccana will be merged, with the resulting server retaining the Set name. If character name conflicts arise, they will be resolved based on account status (with actives given priority), character level (higher levels get priority), and account age.
Guilds will keep their names but will have their server-of-origin name appended. Guild cities will retain their playfields and spots, with new instances being created when necessary. Battlekeep spots will be cleared, and currently, occupying guilds will see their resources reimbursed. Hit up the AoC forums for further details.