So, I traded for an ethereal CtA a while ago, and as a smiter I quickly regretted doing so. Every so often I would accidentally attack with my CtA equipped, and the durability would take a hit. It got so bad that at 3 durability I told my friend, a sorceress with a low level CtA, that I would give my CtA to them when I hit 1 durability, thinking the CtA would be useless if it were to hit zero durability.
Well, tonight I finally broke the thing by accident, and it still works! Not only that, but now I know right away when I accidentally have it equipped because of the red weapon alert on the side of the screen.
Posting this here in case someone might find it useful.
Tldr; Eth CtA doesn’t “break” when durability goes to zero