Your floor slab is not your foundation. That's under the bearing
walls. If the plumbing is run under the footings, I'd be really
concerned, unless you're on exposed ridge.

Can't say about the plumbing. Depends on what they do to get at it, and
what it's made of. You might make mention of the fact that you'd like a
second set of eyeballs to go over it before closing it up.

Got a camera ready?

HTH,
J