Roots under shower pan

[Dan Garvin]

I just tore out the old shower (fiberglass unit) over a concrete slab and found roots around the ABS riser pipe. I'm planning on putting down a sloped concrete bed, liner, and mortar pan and tile above that.

Question is: Should I dig out the roots and old pipes and replace them before moving on or if the drain is working just leave the roots?

I do all my own work but I'm not an experienced plumber. Looking for some advice on how the pros would approach this. I don't mind the time and work of tearing it out so it's not so much a cost issue. Just don't want this to come back and bite later. I only want to do this bathroom once. Here are some pics:

 

[Terry]

I saw something like that under a slab in a big shopping mall one time. I made me wonder if the concrete had been poured over a pasture.
I think I would cut back what you can and then forget it.
Anyone else have an idea?