Cutting a hole in a concrete floor is virtually certain to cause cracks.
They will cut with a saw and will leave sharp corners. Corners are "crack starters". You will have cracks going out from all of the corners. Even if they round the corners you will have cracks. And the joints will crack. No joint is ever as good as the original continuous concrete.
If you ever tile it, you will have massive problems without special processes. It could even be a problem with other types of flooring such as vinyl or wood.
The plumbers Errors and Omissions insurance should cover the cost of a new slab that extends to the OUTSIDE of the foundation and is tied to the foundation. The only joints should be outside the floor area and new concrete should be tied to old concrete with adequate steel reinforcing.
If they talk you into accepting the floor, then make them give you a fully prepaid, securely bonded transferable warranty, at least 20 years, that will survive their bankruptcy, to fully restore and repair any damage to the floor and consequent damage to anything else that is in any way associated with cracks and joints in the floor.
Otherwise, get them to give you a big discount in addition to repairing the floor. Then you will be able to pay to fix the problems later.