front struts dead and just running on coils
I don't think that will cause the springs to sag - as a general rule, coil springs do not "weaken" with age and usage, at least, not in the way that leaf springs will (I know engineers who will argue that it is not possible, but I have seen it happen, so I know it does).
I can understand it happening if the springs are severely overloaded - winch, bumper, dual batteries, skid-plates, etc., which was the reason for my earlier comment about unmodified vehicles, and the picture shown does not show anything of this nature.