Just bought back a written off car and its pretty simple.
They offer you an amount as an insurance payout - haggle as much as possible to increase their offer. Normally a look through P/H or autotrader will provide examples of cars similar to yours from which you can use to prove the valve.
Once you accept their payment you can agree a buy back price (as long as its a Cat C or D write off you can buy it back- Cat A must be scrapped and Cat B can only be purchased by breakers)- In my case the car was a Cat C so they wanted 25% of the payout to buy the car back. ie They gave me an 8K payout and it cost 2K to buy it back.
Fix the car, it should cost a lot less than the estimates they receive as you can use second hand parts to fix.
There's no requirement to MOT the car (if it has an existing MOT) to get it back on the road. You can get a VIC check to confirm the vehicles identity (costs £40) you don't 'need' the VIC check but you wont get automatic tax reminder in the post and i guess it may be more difficult to sell on as and when. The only thing you MUST do to get it back on the road is inform the insurance company. Most insurance company's will insure a written off car but there is a couple that wont.
It can be quite a good deal to buy back depending on circumstance

but do the math first.
On the bodyshop, i very much doubt it'll be fixed so it won't really matter. However as i understand it the higher the quote to fix the greater chance it'll be a Cat C write-off. So going to Audi will probably increase the cost to fix and therefore chance of being a Cat C.
Gutted for you
