95, 525i hit water worked for 1 month now dead?

My son ran into a puddle at the lower door level, some water wet into the back seat. The 525i initially stalled but started back up immediately. It ran rough for a day and the O2 sensor was damaged and replaced by BMW dealer. About one month after the water incident the car began failing to start Intermittently. All lights on the dash come on but no sound at all when you turn the key. Initially if I waited between 1-12 hours it would re-start. Now it will not start at all. The windows would initially fail and if that happened then it would not re-start. I noticed that across from the back seat there is a black electrical box with lots of fuses and wires going into it. If this was exposed to water is the car totaled? Is it worth fixing a 95, 114K miles car. My fear is that the diagnostic costs from the dealer may be cost prohibative and the problem may be unrepairable. If totaled is there some means to sell the car, because if it start it has a good engine suspension and brakes.

Frustrated, any advice would be greatly appreciated.