Yeah 1 can work just as good as having 2 but when you have none your libido is none existant. Then if you have none as a child you need growth hormones (same if a girl is missing her ovaries they will never develop breasts etc)
There are things that can be done for men without testicles to mainain a sexual relationship but the desire is not there apparently. Obviously if a young boy was to loose both they need hormones also once they reach a certain age as they will be feminine looking and don't develop like the rest of their peers. Obviously fertility is a massive concern but I think for a young man saving future Libido is even more important. I really hope he will make a full recovery from this and it not effect him in anyway.