As of yet, Starz and Sony have only commissioned up to season 6.
Sam Heughan and Caitriona Balfe signed 7 year contracts. Not seven seasons. Season 6 will be their seventh year of filming.
Lord John is not seen in the 6th book. And possibly David Berry only signed on till season 5.
If the series gets more seasons, which as its Starz biggest money maker, and if the two main leads are willing to carry on, it may well do, then David Berry may well be seen again.
For anyone one who has read the books knows, Jenny Murray takes a major part again in later books and Ian Murray senior makes a brief appearance.
Neither of the actors who play them are still under contract I dont think. Laura Donelly didn't appear in season 4 as she would have in the books. And she has just signed for a new series. And Steven Cree is now that series about witches, so maybe they will be recast.
And can you now tell I am far far too invested in this programme after being locked down since early March 😆