ApocalypseTale(My own AU)

A skeleton recovered

"And that's how Sans got stuck in a knot in a tree!" Papyrus exclaimes to his friend, Nightmarrow, or Lady Nights, as he calls her.
Nightmarrow chuckles, "Oh wow Papyrus. Sans seems like a great brother though."
Papyrus nodded, "Yes. He is. Though he is very lazy." Suddenly, they both heard shouts from outside the bases' fence.
"GET THE FUCK AWAY FROM ME YA DAMN WALKERS!!!'
"Wait...that sounds like...SANS!!" Papyrus exclaimes and ran to the gate of the prison. Sans bolted through trees, using a handgun against walkers as he ran, Papyrus ran out to get him.
"SANS! YOUR ALIVE!!" Papyrus shouts as he runs to his brother. They run towards the fence, Sans, normally slow, is acually faster than Papyrus on this.
"PAPYRUS?! Bro what the hell?!" Sans exlcaimes as he runs. They both get into the prison. Sans is panting a bit but doesn't show it. His right shoulder doesn't look like his left.
"Brother? Is your shoulder alright? And the rest of you! You don't look that well!" Papyrus asks his brother, worried.
Sans tries to shrug, but immediately grabs his right shoulder and nearly doubles over in pain. Nightmarrow runs over.
"Here! Let me help!" Nightmarrow's hands glowed white with white magic and healed Sans' shoulder, and other wounds he has.
"Thanks.." Sans says and standsstraight, his shirt was torn at the chest, showing some of his ribs, and at the sides slightly. He has a fresh scar across his mouth as well. He's also very skinny. Suddenly, a squrriel, somehow has mostly black fur, climbed onto Sans' shoulder.
"Black Trail still lives?! After all these years?!" Papyrus exclaims, wide-eyed. Nightmarrow tilted her head confused.