I love teaching this story, even though I'm continually frustrated that my students (mostly Southerners who are very closely tied to their home town) side with two of the characters (Mama and Maggie) and have little or nothing that is good to say about Dee. They see the characters who stay home as the ones who are being true to their heritage and see the one who leaves, changes her name, etc. as the one who is failing to value her heritage. I suspect that if I taught this same story to Northern, urban people, the reaction to the characters would be different (if not the very opposite).
My point here is that the story can (and should) be read differently. I would encourage you to think twice about any easy summaries and interpretations of the story that you might come across.
To answer your question, finally, you may be able to conclude that there's not simply one way to be true to your heritage. You can stay where you (and the generations before you) were born and raised, or you can leave, taking your heritage with you, remaking and revitalizing it as you move into new realms.
Alice Walker is an artist and a strong believer in the refashioning of heritage. At least a few critics have argued convincingly that she more closely resembles Dee than she does any other character in this story.
If you are concluding an essay on Walker's theme of ancestral heritage in the story, I would discuss Walker's view that ancestral heritage must be personal and practical, as seen in the characters of Mama and Maggie. If someone truly wants to honor his or her roots/heritage, that person will discover the family connections to heirlooms, not just the cultural significance, and put those heirlooms to good use. Mama and Maggie actually use the family quilts, whereas Dee wants to display them. While not all heirlooms are usable nowadays, the idea that Walker presents is that we must know the history of those objects in order to get in touch with our heritage.
One more suggestion--if you have to write the standard narrow-to-broad conclusion, begin it by talking about Walker's view of ancestral heritage (as seen above) and broaden it to the general population.