How are my Unity 5.x projects supported as a Unity 5 Pro Perpetual license holder?

Symptoms

• I have a Unity 5 Pro perpetual license
• I use Unity 5.x
• I expect ongoing support for my Unity 5.x project

Cause

The Unity 5 cycle end date is March 31, 2017.

Resolution

Unity intends to provide bug fixes in the form of regular patch releases for Unity 5.6 until March 31, 2018.
For continuing support and new features, purchase a Unity Pro subscription.