So here’s the answer in the simplest terms I can think of: If you just let the ski run out of oil in the tank, you will starve the rotary valve of oil and destroy the motor. There is a light that alerts you that the tank is low, but there is no switch to shut the motor down before this happens.
If you must remove the oil injection, which is not recommended, you will need to remove the oil pump and put a block off plate in its place. You will still need to leave the oil tank in place and full of oil though, because the rotary valve is gravity fed from that tank.
In my opinion, you are far more likely to mix your fuel and oil at the wrong ratio, or accidentally fill your tank from the wrong gas can, than you are to have an oil pump failure... You’re adding complexity to the system by premixing, not making it simpler...