Without power steering, your vehicle will be much more difficult to steer, especially at low speeds. This could lead to an accident, especially if you are not expecting the increased effort required.
In addition, driving with a broken power steering pump can damage your vehicle's steering system. The power steering pump provides hydraulic pressure to the steering rack, which is what allows the wheels to turn easily. Without this pressure, the steering rack can be damaged, which could lead to even more expensive repairs.
If your power steering pump is broken, you should have it repaired as soon as possible. In the meantime, you should avoid driving your vehicle if possible.