Lifespan of the GTX 1080?

[IAEInferno]

If it is at a stable temperature like around below 70 C, what would be its product life?

 

[basroil]

It will be longer ON AVERAGE than it's useful lifespan, i.e. it should become irrelevant with even a $100 card beating it long before it dies. On average that is.

 

[Chugalug_]

I wouldn't worry about lifespan unless you're constantly hitting above 80c. 😛
You'll be perfectly fine, the card will become irrelevant in terms of performance before it dies most likely.