You are free to pursue the teachings of the spiritual heart for however long you choose and for as long as they continue to work for you. Upon finishing the last discourse (#144), you need to have an active subscription to the Soul Awareness Teachings audio series (SAT) to maintain an ongoing student relationship the Mystical Traveler Consciousness, as well as to remain an active initiate or minister and to apply for further initiations. Remaining an active student also allows you to take classes and workshops not available to the general public.
If you allow your SAT subscription to lapse for 18 months or more after completing the 12 years of Discourses, you will need to start over with Discourse #1 if you wish to continue studying in MSIA. To be considered an active MSIA student you need a current subscription to Soul Awareness Discourses, or if you have completed the 12 years of Discourses, an active subscription to the Soul Awareness Teachings (SAT).