I've often wondered this, haha. If a person were religious on preventative mixed with restorative maintenance, would there be a reason to ever get rid of them (besides lack of part availability and creature comforts).
I'm always amazed (and a bit jealous) when I hear of someone still driving their Model T Ford, 1940 pickup, etc. It's rare, but there are some out there that have held on to them and continue driving them.
Side note - but along the lines of adding new parts: The regional manager for a chemical company I used to work for said he had to add a quart of oil in his truck every couple weeks. He'd pull from the tanker as we were emptying the fluid into the steel mill reservoirs. He said he never changed his oil because he's always adding new. Makes a little bit of sense. And the variety of straight oils that he was adding was probably keeping his engine nice and clean and lubricated..