What ultimately happens when a black hole evaporates due to Hawking radiation?

I hit a snag while trying to explain black holes to my son.

I was explaining that black holes gradually lose mass through Hawking radiation. As a black hole evaporates, its mass decreases and its event horizon shrinks.

My son then asked what would happen if the black hole became extremely small—say, comparable to the mass of Earth or eventually just a few kilograms. Would an event horizon still exist at such scales?

I understand that an Earth-mass black hole would still be much larger than the Planck length, but as its mass approaches the Planck mass, its Schwarzschild radius would eventually become comparable to the Planck length, where quantum-gravitational effects should become important.

At what point, if any, would the event horizon disappear? What would happen to the matter and information inside it? And if the horizon persisted, could the singularity somehow disappear or be replaced by a finite quantum-gravitational interior?

Could the disappearance of the horizon itself be a quantum transition, somewhat analogous to a phase transition?

I realize these questions go beyond established physics, so I'm particularly interested in understanding what we know with confidence, what is speculative, and where our current theories stop being reliable.