Every object in low-earth orbit, left to itself,
decays, or inexorably falls back into the atmosphere and eventually reenters. That's because there is still some atmosphere even 300 miles up in space, and therefore there is resistance which slows the orbiting vehicle down unless it periodically expends reaction mass to bump it back up to its intended orbit (there are alternative ways to maintain orbit, but none are regularly used). Magnetic fields and solar winds also play a role in orbit decay, and probably other processes as well.
Every space station ever orbited (except this one--so far) has eventually decayed and reentered the atmosphere.
Skylab left a debris footprint across a good chunk of Australia.
Mir disintegrated over the South Pacific. The
Salyut stations were generally much smaller and didn't create as much of a buzz when they came down, but they all did.
This one will, too, unless we deem it to be worthy of the expense to maintain its orbit indefinitely, or to kick it up into an orbit so high that it can't come down for decades or centuries.
(Edit: I might as well just come out and say it: Those who don't understand the mechanics of space travel are
always the ones who want to spend that money here on earth, instead. Then they drive their Kevlar-and-plastic cars home, unzip their Velcro flies, slide onto their polyester-stuffed couches, and watch satellite television, safe in the knowledge that space travel means nothing to them.)