It might not place neighbors at appreciable risk but wouldn't debris still prevent replacing the failed satellite with another one at the same precious original address?
No, because the debris = tiny pieces of aluminum, will be pushed around by solar radiation.
Also, there’re tiny meteorites, and other pieces of debris colliding with it, which adds energy to the system, if you like.
TLEs are not maintained for small debris, so you can’t really predict conclusively. But my hunch is that eventually, the orbit will become a bit more parabolic, precession of which could put it into a trajectory of a S/C and cause a collision.
Things in geo orbit aren't perfectly stable, since the Earth's gravitational field is not perfectly uniform. Without active station keeping things tend to gather at two particular longitudes over the equator. So eventually that debris will probably end up at those points.