From your description and photos I would say your overwatering it (thats terrible looking soil for bonsai) and it may not be getting enough light. Ficus don't need a large amount, but a flourescent or south facing window are best.

The white stuff could be deposits from your water, or fungus. It is too hard to tell from the photo. If theres any hint of "fuzzyness" about it then its fungus. If not its more likely to be just deposits (nothing to fret about).

As far as whether it is dead and gone, theres no way we can tell from the pics. I suggest you cut into one of the branches. If it is green underneath then it can be saved. If not it might be gone (though it could be just that branch). You can also try bending the branch instead of cutting. Dead branches break a lot more easily/feel more stiff. But if you don't already know how much bending a live branch can take, you won't have anything to compare it to.