my ficus bonsai's leaves are dying and there is white fuzz on the leaves and branches what could this be? Spider mites?

Could be anything. But this plant is dead.

That is grim news but thank you for notifying me. I will continue to water it for another month or so before I give up completely and start from scratch on a new tree.

"Powdery mildew" looks to me at a glance. But the trunk looks firm, rather than mushy ... so is it dead? If I were you I'd ask around a bit more before I'd start watering it. It could be that excess water was the problem in the first place. Just guessing. It is a common mistake to think that ficus needs lots of water and frequently. Being a tropical plant must be the reason for the misconception but the ficus should be rather dry between watering. I hope that I haven't confused you even more than you were.