Who knows? The need for steering damping is directly related to scrub radius, so it would seem that should be independent of sag at least. Wear will always change the dynamics though, in the sense that less friction in the components means there is more force available for oscillation. If it was easy to design a truck suspension and steering not to need damping then you better believe all the manufacturers would do anything they could not to use them, but yet most trucks come with them from the factory. It could very well be that they put them on for belt-and-suspenders, so that the truck does not become a death trap when the ball joints and TREs are no longer factory fresh and the whole system is no longer exactly like it was engineered originally, when might not have been a need for the damper.
"Silent enim leges inter arma." -- Cicero