When a wheel bearing starts humming, you might wonder how long you can keep driving on it. The short answer: not long, and not far. Here is why a bad wheel bearing should not be ignored.
The real risk: seizing
A failing bearing gets progressively worse, and in the worst case it can seize or let the wheel wobble badly - which can cause a loss of control or even a wheel coming loose. That is why a growling bearing is a safety issue, not just a noise; see signs of a bad hub bearing.
It affects braking and ABS
Because the hub carries the wheel-speed sensor and locates the rotor, a loose bearing can upset the ABS and even the brake pad contact; see bearing vs brake noise. A wobbling hub does not hold the rotor steady.
How long is too long
A bearing just starting to hum may last a little while, but there is no reliable safe mileage - it can go from noisy to failed quickly. Treat it as a soon-not-someday repair, and avoid high speeds and long trips until it is fixed.
Fix it
Replace the hub bearing assembly and torque it to spec; do both sides on an axle if the mileage is high. Inspect the brakes while you are there; see grinding when turning. Keep the brakes fresh with quality pads and hardware.