I'm to old to be anything but a traditionalist. It's leather -leather and more leather.
I have made knives with Cordura sheaths, plastic sheaths, kydex sheaths and consealex sheaths. All my personal knives have a leather sheath. I truly see no advantage in any other materials. If you take reasonable care of a leather sheath it should last a more than reasonable length of time. (now here's where I contradict myself)
Coudura sheaths are stiched together just like leather. In my experiance the stiching is the first to go so I see no advantage in the cordura or lined cordura.
Kydex and consealex sheaths , if made properly for the knife should out last the knife. From a practical standpoint they are most likely the best. If Made Properly. I just don't like that they are loud and look like injected -molded plastic. That is a personal preferance and I already said that I'm old and stubborn. Since they have no stitching The only thing that you could have happen to them is that the sheath could be exposed to heat and melt. I have exposed them to sever cold with no adverse effect. Now that I have told you all the advantages of Kydex and Consealex ,I will say again that I still have leather.( I told you I would contradict myself.)
Mike..........