The thermonuclear situation with North Korea is an existential threat, EMP or otherwise.
Just taking what is being said at face value (taking no political side whatsoever), is China included in the countries whose trade would be sanctioned with the USA? That would put Apple in a world of hurt. As well as many other US businesses. From the Sept 2 Wall Street Journal:
Treasury Secretary Steven Mnuchin said he has spoken to the president about further isolating North Korea economically.
“It is clear that this behavior is completely unacceptable,” said Mr. Mnuchin on Fox News Sunday. “We’ve already started with sanctions… but I am going to draft a sanctions package to send to the president for his strong consideration that anybody that wants to do trade or business with them would be prevented from doing trade or business with us.”
The world economy is so interlinked with China that this interesting idea has little credibility—the world economy would pretty much shut down as huge numbers of products and parts would be affected. So I deem this threat as having little credibility and thus giving the USA little real leverage.
Still, years ago I was thinking just how risky it was for Apple to rely so heavily on one country to build its products, particularly the iPhone. That risk has now emerged as not so far fetched. Then there is the national security risk of having China being almost the sole supplier of rare earth elements (vital to the military as well as iPhones).