Sapphire is a good brand so I don't think you'll need to worry about graphics failure. Provided reasonable care is taken of the PC as a whole, I'd expect ultra settings for about 2 years for most games and settings to be lowered from there as gaming textures and graphics advance beyond it's single card capabilities. At that point you can X-Fire to get another few years at ultra settings (hopefully)
Probably 2-3 years on ultra, another 2-ish years on high. That's just a guess though, it could last longer, or less time. Either way it's stronger than the PS4 or X1, so it should crunch through ports pretty easily for whole the lifespan of the consoles.
It definitely shouldn't break, video cards hardly ever break.