Any piece of electronic equipment can fail at anytime regardless of how it was handled, used and maintained.
I've had a GTX 280 that I used for 2.5 years. I kept it clean. When I got a GTX 570 the 280 went to my younger brother. He used the card for a solid 3.5-4 years and never once cleaned it out. When he finally got some cash to build a new PC, I had my GTX 980Ti and I gave him my GTX 570. The GTX 280 he gave back to me was coated horribly in dust, I'm surprised the card didn't die.
As you can see, the card wasn't the best taken care of GPU, yet it still works to this day. Your GPU may work for years on end and it may fail after a few months....no one knows for sure how long it'll survive. Keep it clean, don't run it for long periods to stress test - that's just rather pointless - and keep it as cool as you can.