Do my digital materials expire after 180 days, or is it just the download link that expires?

If you chose to purchase a 180-day access ebook, both the link from the My Digital Materials section of your store account and the digital materials will expire 180 days after purchase. If you would like to access your book for more than 180-days, you can upgrade to perpetual access before the ebook expires. Simply click the link that says Upgrade to Perpetual next to the ebook in the My Digital Materials section of your account.