I have a 2003 Trailblazer with 299,978 miles as of this evening. Original engine, replaced alternator and battery only. Still has the original brakes, shocks and exhaust. Still gets 22-24 mpg.
Mine's a 1994 model. It turns 20 years old this year. The problem you eventually face is that some things break down over time, regardless of how many miles you put on a vehicle. Electronic components are a good example of this.