The decapeptyl injection is his best chance. The chemo is only a new thing given so early and it MAY help to prolong the efficacy of the implant, there is no certainty/guarantee that it does. The infection he may have had is Neutropenic Sepsis, it can kill in a matter of hours if not found early, it is classed as a true medical emergency. My OH had it and felt fine, his temperature was only 37.7 when they admitted him to hospital. Because there is no certainty that the chemo is helping it is not worth running the risk of getting the sepsis unnoticed and it possibly killing the patient.
Were you with your father? If not could you not telephone the care team and have a chat with them? I am sure they would be happy to explain in more detail, even if your dad had to give permission for them to talk to you.
My OH only had one chemo. He had the Neutropenic Sepsis and was in hospital for five days, when the next chemo was due he had chest pains walking into the hospital so the chemo was cancelled while they checked his heart out, as the oncologist said, the heart has priority over the cancer, at least with the cancer we are hopefully talking in years, if he had a heart attack, well obviously the cancer would not matter much!
No one ever mentioned Neutropenic Sepsis at any point, think they don't want to scare people.
My OH is now 'only' on the HT and I believe he is still on the best treatment available, sadly there is no certainty with this, everyone reacts differently to the treatment and the condition. We do have to put our trust in the doctor, they understand all the medications better than we ever will.
It may be worth ringing the nurses on this site, I am sure they would be able to put your mind at rest a bit and answer some of your questions.