You only change an alternator when it goes bad. I change my oil and filter every 3000 miles,change the fan (accessory drive) belts when they show signs of wear (cracking) I rotate tires every 3000 miles ( do this when you change oil) And you repair a motor as needed (usually it can be fixed rather than replaced) tranny will last a LONG time if you flush it and change filters regularly) Only replace motor/tranny when it can't be fixed.As far as how long will a vehicle last is really a loaded question. I have a transportation business. We use small wagons,mini vans,and cargo vans. I have a Ford Escort wagon that has 625,000 miles on it. original motor and it has never been rebuilt,it has had a tranny swap. I have several other Escorts with over 400,000. I have a 2000 Ford E-150 cargo van that has 435,000 on it right now and the only thing that was ever done to it was the cat converters were replaced twice. If you treat a vehicle good, and maintain it great,.....it should last for a VERY long time. GOOD LUCK!, Rob in PA.