Brain metastasis

To your question, the chance of PCa going to bone is very high unless it is diagnosed early and treated. In your dad's case the chance was 100% since he does have bone spread already. If this is a typo and you were asking about the chance of spread to the brain and / or skull, this is more likely with some types of prostate cancer than others. As your dad has skull mets, it may be that he has a more rare type. You could ask his doctor.