From
Wiki
Death and succession
Following the death in 1971 of Prince Friedrich Günther in Munich the House of Schwarzburg became extinct. However the Schwarzburg principalities operated under Semi-Salic primogeniture which means that in the event of the extinction of all male dynasts, as happened with the death of Prince Friedrich Günther, females can inherit. Therefore if Semi-Salic law is applied then the current heir to the principalities of Schwarzburg is
Count Friedrich Magnus zu Solms-Wildenfels (born 1927) the son of Princess Marie Antoinette of Schwarzburg (1898-1984), sister of Prince Friedrich Günther.
Alternatively another claimant could be
Prince Philip zu Stolberg-Wernigerode (born 1967). Prince Philip's claim is based on a pact made by Count Heinrich of Schwarzburg and his son whereby if his male line became extinct then Count Botho of Stolberg and the Counts of Hohenstein should share the majority of his territories with the Counts of Stolberg inheriting Kelbra and Heringen alone and not share them with the Counts of Hohenstein. With the extinction of the House of Hohenstein the house's of Schwarzburg and Stolberg renewed the pact on January 28 1594. Therefore if the pact is still valid then Prince Philip as senior male line descendant of Count Botho could be seen as the rightful heir.