If my baker accidentally double bakes how much will I be penalized and when can I safely begin baking again?
Currently, as of protocol 003, double baking(or endorsing) is penalized with losing all of one's rewards and bonds for that cycle in which the double bake(or endorse) occurred. The rewards are completely burnt. Bonds are half burnt and half rewarded to the baker that baked the block that includes the accuse operation.
If double bake occurs, the baker should stop all baking for that cycle in which the double bake occurred. Any new further rewards or bonds made for that cycle could be penalized again by the same accusation. Yes, you can get accused more than once for the same double bake! Also, the accuse operation is allowed to be included up to 5 cycles after the cycle with the double bake. This is why all baking should halt after the double bake for that cycle because you are not safe from another accusation until 5 cycles later.
As long as your next bake(or endorse) happen on a cycle after the cycle you had double bake, those rewards and bonds are safe from accusation. But any rewards and bonds for the double baked cycle will still be open for accusation for another 5 cycles.