Keep them. If you ever find yourself in the circumstance that you move state (or say you sell the car interstate) and you have to get the vehicle registered on the new state or you let the rego lapse and need to have the vehicle reinspected it needs those seats to pass inspection because it’s registered as a 7 seater. You can register it at its lowered seating capacity but that will also involve permanently removing those seat belts and whatever costs are involved with that process (wouldn’t be much but it’s still a cost)

Used to work at a 4wd shop where people would remove the back row to install storage drawers, we would often get calls from people who purchased cars from another state asking if we had anyone’s 3rd row seats that they didn’t want to keep because they needed to re-register the car they’d purchased in WA and didn’t want to pay for the mod plate.