broken drain line somewhere under slab

oh no! Aplumber just told me that I don't have a clogged sink but rather a broken pipe about 20 feet along the pipe that connects to my sink. he didn't have a camera so he couldn't do anything, but he hit mud with the snake. He said once we locate the area someone will have to cut out the floor, slab etc to repair the pipe. In the meantime, our family has no working sink! Anyone have this problem? Also, my radiant heat still works-replaced the boiler 2 years ago. Anyone know where the pipe goes under the house exactly? Susan