Until you sign the title over it is your car. You own it. You can take what you want off it. However, if you don't put a factory part back on then the insurance company will deduct the value of the part you removed. Grab a junk yard rear end out of a G8, caprice, Camaro, etc and swap it back. Heck I had a rear end I took to the scrap yard about about 6 months ago because I couldn't give it away! LOL. Hit up CL, FB, Car forums for a granny gear rear end nobody wants. Easy to do in a half day. You also may need to pay the tow bill and storage fees to get it towed out of the lot to some place where you can work on it. Most storage lots don't allow that sort of stuff on premise. Either way be honest with the adjustor if you are taking the car back to stock or signing over the title with missing parts. You don't want to be accused of insurance fraud because you started taking parts off after the insurance company paid out an agreed amount.