Computer parts are not meant to last forever. In the case of graphics cards, you are looking at replacing them in the ballpark of five to seven years.
It is a greater waste to have good graphics card and not use it, than to use it, have fun with it, and have a great, entertaining five years.
In any case, your graphics card is more likely to be replaced because you want a better graphics card, and not because you are running games at high settings and so ruined the card. They are designed to be durable.
In short, please don't worry about it and enjoy the card.