Yes, 'Poldark' is based on a true story. It is based on the novels by Winston Graham which were inspired by real - life events and characters in Cornwall's history.
The Poldark novels are not entirely based on real history. While they use the historical backdrop of Cornwall in the 18th and 19th centuries, with things like the mining industry and social hierarchies of the time as part of the setting, the main events involving the Poldark family and their personal relationships are fictional. For instance, the love stories and family dramas of Ross Poldark are the product of the author's creativity, not real historical happenings.
Well, in the Poldark final novel, it could be very important as it might resolve all the loose ends. For example, the love stories that have been on and off might finally get a definite ending. The characters' growth over the course of the series can be fully realized here. It also might provide a more in - depth look at the historical context that has been a backdrop for the whole story, perhaps showing how the characters fit into the bigger picture of the era as everything comes to a close.