I have first hand experience with this unfortunately.
No, your insurance will not cover the after market parts if your truck is destroyed in an accident. They will only cover the blue book value of it regardless of any aftermarket parts. I have had to deal with this exact issue twice in the past 2 years (once was a county tree falling on my truck, and once was a drunk driver in a MOTORHOME that hit my truck while it was parked), and my insurance tried to screw me both times. However, one thing I did learn, is that you can get your vehicle appraised (like you would a house or jewelery), by an licensed independent auto appraiser, and they will take into account any and all aftermarket parts. They will take a bunch of pictures and generate a complete report with a defined value that you can then give to your insurance company. Then in the event of an accident, with that report, your insurance company will have to cover the appraised cost of the vehicle.
Insurance companies are crooks :imo, they have no problem taking YOUR money, but when they need to give some away....the will find any and all excuses in the book to get out of covering you, regardless of how big or small the issue is.

issed: :yourself: State Farm...