It looks like it got punished by lack of water. Keep it well watered and see what comes back. You really can't leave a potted tree unwatered for more than a few days. In hot weather you pretty well need to water them daily.

I'm not sure about the white fungus. There's a chance that your trees root system or vascular system has been destroyed by a fungus, but they don't usually present like this. Given what you said about not watering it I think that's the most likely problem.

This one got dry. It is in shock and will lose its leaves and grow new ones (provided it is still alive.) You can snap a stem or small branch and if it seems green, you may be good to go. Just keepnit watered and out of the hot, hot sun.