I know that the German ducal house of Saxe-Altenburg is. But the other Saxon dynasties -- royal and ducal -- still survive (I believe). However, I'm less certain about the grand ducal house of Mecklenburg: evidently the Schwerin branch (of which the late Queen Juliana of the Netherlands was a male-line descendant) is extinct. But the Strelitz branch survives, headed by some Borwin. What's the exact situation with the succession in this dynasty?
Obviously the non-reigning houses have all had to modify their marital standards (such as the requirement or qualification for *equality*), in order to survive. It's much more difficult to amend a succession law which either excludes females entirely (i.e. Salic) or grants them limited rights (i.e. semi-Salicism). But this did not stop the late King Michael of Romania from trying to change the law in order to permit his daughters to inherit his royal claim (notwithstanding the fact that the throne is long defunct), although only after consulting the other members of the house of Hohenzollern-Sigmaringen (who do not appear interested in pursuing the said claim themselves).
More recently, the Duke of Savoy made news by attempting to change the Italian royal succession law, so as to allow his granddaughters to inherit the claim. In this, he was being like the Duke of Castro, married since 1998 to Camilla Crociani but having no son. Despite the royal house of Bourbon-Two Sicilies operating under the semi-Salic succession law, and despite the existence of other dynastic males, he presses for the eventual inheritance of the claim by his elder daughter, Princess Maria Carolina.
Certainly no dynasty is in danger of extinction if females are, under official house rules, permitted to succeed when there are no eligible males: such is the case with Russia and Saxony. It's too bad that Romania didn't operate under the semi-Salic law. For in that case, Princess Margarita would be the undisputed claimant ...
Anyhow, Salic law or otherwise, I was wondering about other notable examples of extinct dynasties.