Jun 03, 2019 - 07:01 AM
In it's simplest form, an evergreen license model can be seen with some personal software subscriptions. The most common I know of is an Office 365 subscription. Each year I receive an email (that I always overlook) that lets me know that my subscription will automatically charge my payment source when the term ends. This is a prompt for the user to cancel the subscription before it automatically renews.
Similar evergreen clauses can be seen in larger enterprise software contracts, so it is always important to review the Termination clause of your contracts. Some may require an "intent to terminate" communication to your account rep several months before it auto-renews. Make sure that if you are going to terminate, that you have confirmed that all use of this software has ceased, and installations are removed. This could prompt an audit with the vendor.
Whether these clauses are enforcable is up for debate. As you said, there isn't a lot of documentation online to help outline this broad topic, but I did find this article somewhat helpful - License Agreements: Evergreen Clauses