Pathfinder Adventure Paths in Mystara
by Giampaolo AgostaWar for the Crown: Eusebius could die before Thincol, but Thyatis is not really feudal. Karameikos could work, since Stefan's heir is Adriana. Otherwise, Eusdria is a feudal nation and I don't think the king has an established heir.
Hell's Rebels and Hell's Vengeance: while most Mystaran nations are not ruled by "evil" monarchs (even less by devil-worshipping ones, since devils don't appear in the setting), most rulers are not really good either. Several have to face resistance movements which they characterize as terrorists, but could be equally seen as freedom fighters instead. Beyond Hule and the Heldannic Territories, we could consider Karameikos (especially in the early years), Minrothad (Oran Meditor was the target of at least one assassination attempt and the government is definitely not nice), and Glantri (there are several terrorist groups, from ELF and FAIRY to the Followers of the Claymore and the werewolves).
Giantslayer: as far as I understand, this is PF's take on Against the Giants. The Northern Reaches could work, but if a wide variety of Giants is needed, probably Norwold would be better since it provides a wider space.
Tyrant's Grasp: There are several liches in the Known World, including at least two canon ones (Brannart McGregor and the Nithian Lich in Alfheim).