NPC Guild cities - great idea! They would be controlled by a level of AI, but when attacked, online Guild members could be notified and come to its defense. Guild treasuries, as well as POWs and any "special bonuses" picked up by guild members could be "stored" there. And plundered from there.
However, delaying battles - Big no-no. Online players will want battles, and having them wait for them is a horrible idea. Still, NPC Guild City -WOW!