I don't yet have the Westone 3, but I do have a UM2 that I've had since 2006, and I do not baby the UM2. I've slept with it on many occasions (it's one of the only headphones I can wear while sleeping, because of how flush the UM2 sits in the ear's concha). I've inadvertently tugged at its cables as much as I have any of my other earphones. I tend to store my UM2 by essentially rolling it up into a ball or wound into a coin-diameter coil.
I'm of the opinion that the cable is generally more durable than most, as it's supple enough to simply bend as needed, as opposed to kinking. Mine has also exhibited no memory, always unwinding virtually perfectly straight, no matter how tightly I've coiled it, balled it up, etc. I think this also ads to the durability.
From what I understand, Westone has used the same cable in the Westone 3, and, as in the Westone UM2, it's not removable, which I also find a positive. By routing the cable directly into the earpiece, there are fewer stress points, and no strain reliefs necessary (and its more compact, which is another reason the UM2 is the only earphone I have that I can comfortable wear with the side of my head on a pillow). In fact, if I could have opted for this very same cable to have been used on my UE-10 Pro and UE-11 (including the non-removable aspect), I'd have opted for it in a heartbeat.
I would guess that overwhelmingly most who've actually owned the UM2 for a while would agree that the cable is actually among the more durable used in any earphone; and if Westone used it again in the Westone 3, I think it's a great decision.