Our cat was hit by a van about two years ago and, at first, the vet was unhopeful that she would live over the weekend-she wasn't passing urine by herself and her lower back was broken. However, she rallied and, though nothing could be done about her back injury, the vet later amputated her very long tail ,which was just dragging, to save it getting caught up in fences, bushes. You should see her now - she could beat a leopard at running and she jumps up on walls and window ledges with no trouble!
However, we do notice that she sleep perhaps more than a young cat does and, at the end of a day's stalking here and there, one can notice her back sagging at the back.
She still has little "accidents" regarding passing urine but she happily sleeps on a sheepskin in her carrier at night and things seem to get better with each passing month.
Try not to worry too much - remember cats have nine lives!!
All the best.