Seems a bit overboard for a traffic ticket that the other driver was 100% at fault for. They reduced his fine at the scene, and he is still fighting it, really just seems like a waste of everyone's time over a $150 fine.
If you don't show up, they'll likely drop the charge completely. His $150 fine goes to $0 and more importantly, he'll avoid having a conviction. Without the conviction he'll avoid a possible surcharge by his insurance provider (e.g. 5%). If he's convicted again of other offense (e.g. speeding 10km), the surcharge will likely increase with a second conviction.
In the long run, it may save him several hundreds of dollars if not more.
Do you have any idea what happens at the court, what do they ask me and the other people that were in the car ? Is this a full out trial, that takes all day ?
It wont take all day, but it's not something you can do during your lunch break.
He may not even go to trial. He might be counting on you not showing up. He can always just take his reduced fine and go home.