Once the wear sensor light is activated this indicates the wear sensor is in contact with the disc and is now beginning to wear itself, so yes it will need to be replaced.
There is pad still left so you can continue to drive but you answered your own question depends on driving style how long.
A lip on the rotors indicates they are also worn and the only way to be sure about replacement is to measure the thickness and check the minimum.
My view is not to skimp on this area as along with steering they are the most important part of any vehicle.