'Crush' is a misnomer--it doesn't crush. The washers remain as ductile as when new, and its ductility is what allows it to flex to seal the joint
when properly torqued. The only reason to replace one is if it has been scratched, has had grit pinched into the bolted joint (so it has circumferential grooves ground into it from tightening the drain bolt), if nicked, or otherwise gotten mechanically bent or tweaked by something other than being pressed between a clean drain plug and a clean mating surface on the pan. If used properly, the washers can be reused over and over (I flip mine over every time). But they're also cheap and easy to replace if that salves your conscience.
Easiest way to verify the washer: inspect for oil drips around the plug before removing the plug for an oil change. It is normal to have a slight oily dust. But if it is slightly wet (with oil), definitely worth changing the washer.