Most of the above dilemma will depend on what category of a write off it is, which varies according to the price of repair against value of car, and the likelihood of affective repairs being satisfactory to return the vehicle to a proper roadworthy standard.
seeing as it was sufficent to deform the boot floor, i would guess it is going to be about a B class write, uneconomical and tough to repair, maybe, just maybe, if you can negotioate the estimates down in price you may get it low enough to fall into a C, which is at which point it becomes more of a possibilty to purchase the car off the insurance company at agreed market value, less the estimate cost to repair.
so for example the car was worth £3000 pre accident, is going to cost £2000 to effectively repair, you can buy it for £1000 with the insurance compensation that you are offered to consider the car a write off.
it can get a bit tricky from here on, because the car will be on the register, most insurance companies don't mind, but some can add to the premium because they consider the car more awkward to repair and value, should something happen again in the future, so you can sometimes come across an inflated premium, plus because of the classification of write off, when you do finally want to sell it, it is worth very little if HPI'd, and more difficult to sell on altogether.
it can be done but its tricky to get right.
what you really want is to get estimates that are very expensive to make the purchase price very cheap, but go too far and they simply won't do it anyway, but it can work.
a friend of mine did this very thing not long ago with his e320 cdi, quite successfuly, after a side swipe that was estimated to reqwuire entire replacement doors, wings, sils, 2 x amg alloys etc etc, was mostly repaired using all the existing panels after buying it off them at a very cheap price, BUT, it will always be a very cheap car from now on,
so its a balancing act and how much you love the car at then end of the day.
ps - one final note, never accept a first or likely even a second offer, if you can evidence that they have not offered enough to affect the repairs or replace the car etc, you do not have to accept it. the bartering does stop eventually, but haggle like hell, it gets you a lot closer to what you want.