I think the series would be a remake of just the 1989 film, disregarding all the following sequels. It would still follow the 17th century witch hunter, Giles Redferne hunting down the titular warlock (although the warlock would get a name and more of a backstory). Kassandra would still be in the story as well. I think it could still end in the same way, or be rewritten to have Giles stay in the future if they wanted to do a second season.
