The revenge button the way it is now it virtually useless. It is almost impossible to get revenge on a player. So I have two ideas, not mutually exclusive:
- Let´s us mark a player for "revenge". Once he goes offline you receive a notification (maybe a popup screen asking if you want to attack him now)
- On the report screen (where you see your defenses) show who is online/offline and how much time since logoff (same information as appear on alliance gate)