Sorry to hear about your dad, Qesh. I don't have any personal experience to impart but here's a bit from patient.co.uk that explains a bit about symptoms/prognosis:
"How do symptoms progress and what is the outlook (prognosis)?
The symptoms of PD tend to become gradually worse over time. However, the speed of progression varies greatly from person to person. When symptoms first begin, you may not need treatment when symptoms are relatively mild.
Most people with PD can expect to have some time of relatively mild symptoms, and then when the symptoms become worse, several years of good or reasonable control of the symptoms with medication. But everyone is different, and it is difficult to predict for an individual how quickly the disease will progress. Some people may only be slightly disabled 20 years after PD first begins, whereas others may be very disabled after 10 years.
Research into PD is active. For example, one main aim of research is to find drugs that prevent the damage to the affected cells, rather than just treating the symptoms, which is the main value of treatment at present. Further research on these chemicals continues. Research is also underway using stem cell therapy to help treat PD.
Further help and information
215 Vauxhall Bridge Road, London, SW1V 1EJ
Helpline: 0808 800 0303 Web: Parkinson's UK - The support and research charity - (formerly Parkinson's Disease Society)
Provides help and information on all aspects of PD. There are many local branches too."