Nice neighbor! Is the rot spreading? If it is just callousing because of a bruise, I think it will recover. May take a while before new growth continues.I'd keep the body as dry as possible, while making sure the roots do get appropriate water.
I once had a gymno cactus bitten in half by a stupid dog. It took all summer, but, it overgrew the bite and next spring it looked like a normal cactus ball with a horizontal scar.

I wanna step on your neighbor! ð¡

thank uou for the advice, I was very aware that when hurt the cacti like us are very susceptible to infection. so I didn't even move the gravel on thw cut. I left it be. it's not been watered yet. but I'll water it from below.

I have seen others posting about animals eating and cold snaps and then posting that it's taken a while but it's growing again so I am rather optimistic
thank you