A differential leak should be checked promptly. Whether the vehicle can be driven depends on the leak rate, lubricant level, and whether there are signs of damage. A small spot on the ground does not reliably show how much fluid remains inside.
Driving with insufficient lubricant can damage gears and bearings. Do not assume that a quiet differential has enough fluid or that adding lubricant makes an active leak safe to ignore.
Contact Certified Transmission in Council Bluffs for guidance. If you notice substantial leakage, grinding, binding, or severe noise, stop driving and arrange assistance.