You have to do it. There is no way around it.
You can't live your entire life in fear. You realize you could get killed by a drunk driver during the day too, right? We can die at any moment in our lives, so we shouldn't live a limited life because of this fear. I'm very sorry about the death of your dad, but you're gonna have to get over this fear.
It wasn't the dark that killed your father, if he wasn't driving, he'd still be here. You seem to have no problem with driving, so get over it and drive in the dark. You aren't always going to be able to choose when you drive.
Check the requirements closely. Maybe you can drive at dusk, which shouldn't be too bad.
You cannot always drive in daylight. We all have to overcome our fears. You need to drive sensibly and just watch for other drivers. I like driving at night when it is quiet.
Learn the bus routes - because without driving at night your only option will be buses or taxis and the later is really expensive.
driving 15 hours at night? sounds creepy. you may want to check with the police