Intuit's communication does not indicate that PTO subscribers will be provided free access to alternative tax products.  Someone on the PTO FB group spoke with Intuit and was told she'd need to pay separately to access PS if she needs to prepare pre-2013 returns after those years are taken offline.

https://accountants-community.intuit.com/articles/1745873-faq-for-decomission-of-prior-year-tax-retu...