We are currently brainstorming a solution for this and have several options in mind, such as placing an NPC that will maintain the battle status and once the player returns, they can load the status by talking to the NPC to confirm the result. In any case, it will require updates on various parts of the game system and will require some time so we would like to further discuss it internally.
This is a good idea, but you should seriously a core system change, even if it's significant work, to accomodate things like connection issues- like not require that the player be logged in in order for any state-based information to be maintained, and to enable the possibility of players remaining part of a party when they get disconnected (Just show an unplugged cable icon by their name or something). In World of Warcraft, players are not removed from a party when they get disconnected. I really, really wish both FFXI and FFXIV could implement this.