Usually when a car breaks down and can't continue on it's own it will be towed to the owner's own garage. However, in case of a breakdown abroad the road side assistance will always try and fix the car if this is possible within 2-4 days. Transporting the car to the Netherlands is very expensive that is why in these cases a repair is more effective.
If a repair is possible you will always need an approval by the owner. Never approve the repair yourself if you have not yet contacted the owner.
Closing the booking
Normally, you’d be in charge of checking the fuel gage and mileage at the end of a booking. This is a different story in case of a breakdown. It’s important to stay in touch with the car owner on this matter so that you can work something out for the fuel level and mileage.