Ahhhh sorry to hear that!
My cat Jessie (rip) got hit by a car twice and survived both times!
The first time was really bad, the car ran over her hip. My Mum nursed her back to health though by making a warm basket for her (like you have done) and just keeping her food and water and litter very close and letting her take her time to get better, over a couple of months. Apart from a bit of an achy hip every now and then though she fully recovered and lived to the ripe old age of 16!
EDIT, just read the sad news, how awful!!!!!!!!!!!!!!! RIP