Sorry you have to joon this exclusive club, but this is the best place to get info. It would help if you included more stats of your father's situation in the signature.
Your father has a "locally advanced" disease. It sounds like stage T3b. There are several here on the site with this stage. Mine is T3a, a little less spread, but still an advanced cancer.
In a month or so after surgery your dad is going to have an all important PSA test. If it shows PSA under 0.1 then he will have a few choices, if more the choices are fewer.
First, take a deep breath - this is not the end of the world. He will most likely enjoy many more years. Your being calm and supportive will go a long way. Now to the choices. (Guys with more experience will correct me if I misstate anything).
If PSA is undetectable after surgery (less than 0.1) he can wait to see if PSA will go up. The advantage of this approach is that he has time to heal and that sometimes no further treatment is needed. This is called salvage therapy and is usually in the form of radiation (with or without hormon treatment). The other alternative is an adjuvant therapy (same as salvage, usually radiation). The advantage is earlier intervention, the disadvantage is that it may stop healing progress.
If his PSA does not go to undetectable then hormon therapy is likely in his future, with or without radiation.
While everybody reacts differently, radiation is usually not to bad with few side effects. In my case, I am 36 treatments into a series of 40 and am feeling fine. I am a bit tired, but not enough to keep me from doing everything I used to do before, including full time job.
Don't panic, post your fathers stats (age, PSA at dx, % positive cores at biopsies, Gleason, pathology report, etc) and stick around - there is a lot of collective withdom and compassion here.
Finally, even aggressive PCa is moving slow, let your father take time understand the choices, talk to a few doctors to compare their views and only then make a decision.
Father died from poorly differentiated PCa @ 78 - normal PSA and DRE
5 biopsies over 4 years negative while PSA going from 3.8 to 28
Dx Nov 2007, age 46, PSA 29, Gleason 4+4=8
Decided to participate in clinical trial at Duke - 6 rounds of chemo (Taxotere+Avastin)
PSA prior to treatment on 1/8/2008 is 33.90, bounced on 1/31/2008 to 38.20, and down at the end of the treatment (4/24/2008) to 20.60
RRP at Duke (Dr. Moul) on 6/16/2008, Gleason downgraded 4+3=7, T3a N0MX, focal extraprostatic extension, two small positive margins
PSA undetectable for 8 months, then 2/6/2009-0.10, 4/26/2009-0.17, 5/22/2009-0.20, 6/11/2009-0.27
Salvage IMRT + 6 Months ADT: Casodex started 6/12/2009, Lupron 6/22/2009, PSA 6/25/2009-0.1, T=516, 7/23/2009-<0.05, T<10, IMRT to start mid-Aug