If Zhang and Chen flee to China, what difference will it make to Apple? Whatever trade secrets they've memorized could be passed along in a phone call, and presumably already have. Assuming that the files and photographs were already recovered when they were arrested, those trade secrets wouldn't go with them to China.
If they're accused of stealing secrets chances are they have already transferred everything to whoever paid them, but if they go back to China there is no way they'll be brought back to the US for the trial.
The secrets are gone, but at least if they face trial and found guilty they'll be punished for being spies, it is better than nothing.