Elevators cause the aircraft to rotate around the pitching axis, nose up or nose down. If the aircraft is at 90 deg bank, then this pitching axis is making the aircraft turn. But at 90 deg bank, you are headed for the ground, none of the generated lift is pointed upwards, so the weight wins. (But you still needed aileron to roll to 90 degrees).
In any turn, you will be using a little back stick anyway, as you need to generate more than 1g worth of lift whenever the lift vector is not vertical. 60 deg bank, 2g, and then 72(I think) for 3g and then tear the wings off as the bank angle increases. You need infinite g at 89-89.99999 degrees.