Forget about the nuclear plants - after just a few hundred thousand years (an eye blink, in geological terms) you'd not find any signs of damage that might have been caused by unattended melt-downs.  However, nature would still be doing her stuff.  The one thing that everyone who has an interest in geology shares is an appreciation of the time scales involved.

Life on Earth isn't likely to die out until the core cools down and solidifies, at which point we'll probably loose our protective magnetic shield resulting in our atmosphere being stripped away by the solar wind, as appears to have happened on Mars.