1998 Toyota Rav4

That's really hard to say. It depends on how long the cv joints have been without their vital grease (centrifugal forces really spew the grease out of the joint) how much dirt and water get into the joint and to a point, your driving habits. When the cv joint makes a clicking or rattling noise while accelerating from a stop or slow speeds with the wheel turned, it is already too late to save it- you will need a new axle. Catastrophic mechanical failure is hard to predict but if it does occur it always ruins your day.