Getting disconnected during an instance or PVP can be a real bummer. The best method I know to recover from an inconvenient disconnect is to to open a new copy of wizard. Once you have logged in on the same character then shut down the other copy by pushing the X button on the title bar of the window or closing it in task manager. You may want to leave it open and disconnected while you finish what you were working on.
I have found this will USUALLY keep you in your battle or instance.