The service or oil change depends on each car and the specifications of this according to the manufacturer the ideal would be that you consult the manual! There are some services that are made every 15000 as there are others that are made every 5000 that varies.
What you have to have as a rule is to change the oil and air filter oil 1 time per year regardless of mileage. I mean that if the oil did not comply with the mileage but complied with the year yes or if they change it.
That depends on the brand and model of your vehicle, since if in the owner manual it tells you that you must make an oil change to every 5,000 km for example, you must do it, since according to the manufacturer the oil after its km already traveled, the oil loses some lubrication properties, anticorrosive protection among others. It is others to say that the engine may also suffer long -term damage.