Are the total deposits slashed, or just the deposits for that particular block? Also, are these coins then burned? If not, what happens to them?
Nothing happens until the double-baking activity has been denounced
Once denounced the deposit is slashed and if the baker continues to bake in the same cycle his other deposits can be slashed as well. For this reason bakers who happened to double bake during a cycle should stop all activity for the rest of the cycle asap.
More info is available here (section on Accusations at the end):
This accusation forfeits the entirety of the safety deposit and future reward up to that point in the cycle. Half is burned, half goes to the accuser in the form of a block reward.