I was under the impression that a car is only 'written off' (total loss) by an insurance company. As your not going through an insurance company, the car wont be 'written off'. What everyone means is the damage is likely more than the car is worth. In which case you can choose to scrap it or sell it as salvage.
Personally id just get a new bumper, bonnet, replace the driveshaft (and other mechanical bits) and hammer the car back into shape. Most cars dont drive straight anyway. If your not selling it who cares? Sure it will effect the resale value being badly repaired, but if you need a car then its a good solution. Ive never had an MOT station check the chassis for damage before, so it will be fine.
I crashed a 340 volvo once and just sledge hammered it back to shape. Drove just as badly after the crash as it did before. Did another 40k + trouble free miles in it. It looked a lot worse than that one after the crash. Passed a number of mot's without question.
People have this big problem with driving damaged cars. Most race cars have been crashed more times than you realise, and they just get banged back into shape. Most cars are cheaply repairable to a safe standard if you use some common sense and dont mind driving around in a car that doeant look like its just out of a show room. An bonnet can easily be hammered back to shape.