In Shadow of the Giant Peter sends an email to Valentine noting Graff's and Rackham's deaths:
I knew Hyrum Graff and Mazer Rackham very well before they died, and you treated them with absolute fairness.
However, in Ender in Exile Graff sends Ender an email including this:
The passing of your brother must have come as more of a surprise. He was young, but his heart gave out. Pay no attention to the foolish rumors that always attend the death of the great. I saw the autopsy, and Peter had a weak heart, despite his healthy lifestyle.
So who really outlived whom here? Or is some kind of time-travel going on?
Edit: Major spoiler from Xenocide:
"I thought I'd never see you face to face again," said Ender. "You died so long ago." "Never believe a rumor of my death," said Peter. "I have as many lives as a cat. Also as many teeth, as many claws, and the same cheery, cooperative disposition."