My dad's funeral was this summer. Hardest funeral I ever had to go too.
He passed away from cancer so there was no "wake" as he did not want others to remember him as ill. And since he was not religious, he had a very relaxed funeral ceremony that was actually called a "celebration of life ceremony"
The amount of people that showed up to give their support made me feel happy to know that my dad touched so many people's lives. It's kind of overwhelming since I did not know most of the people, but appreciated their kind words nontheless. It was nice to meet people that my dad knew as well.
Funerals are mainly for closure. It's an integral step in accepting the fact that someone has passed and is not coming back. It's a time to cry but to pay respect for their life.
In my opinion, if you were really a good friend of his, or even a friend at all, I would say go. Maybe don't stay for the whole thing, and maybe don't go to the burial if there is one afterwards, but atleast show up and give your respects. Your friend would really like that, and his family will appreciate it as well. Since he was in a bad accident you probably won't physically see him but seeing the coffin is usually enough closure to accept their loss and move on..
what's the worst that could happen if you go? what's worse is that you may regret not going and there's nothing you can do about that after the funeral.