Vehicles are repairable writeoffs when the repair estimates are around 70% of the vehicle value. Vehicles are statutory writeoffs when severe structural damage has been done such that they can not be safely repaired (within the insurers 70% cost constraints as anything can be safely repaired if cost is no option).
In your case, the vehicle damage doesn't look bad at all. There are no pictures of rear door gaps but i'd expect they are unlikely to be altered from the pre crash gapping. In fact, the damage looks more like a low speed love tap (a low energy impact) despite the exhaust being pushed forward. All you need to ensure the repairs are done well.
Remember, the front and rear of modern vehicles are designed to flex in and then back out with minimal damage so the vehicle remains drivable. This is up to some low speed 5-10mph? Larger impacts will see the crush zones come into effect and they don't spring back.
The standard offset crash test is 48kph into a solid immovable block (with some crush pads attached) and the vehicles front squashes about 1/2m. It's violent. Compare that to the pics of the lexus and your car who's damage look nothing like an 48kph offset test.