It can be said that every country that has ever had a monarch still has a hypothetical monarch, to whom the same selection rules apply, unless the whole family in question has been extirpated. The latter is almost impossible to achieve, as the cases of Russia and Ethiopia prove. There are probably collateral descendants of the first (Julio-Claudian) Roman Emperors alive today, although it must be exceedingly difficult to identify them.
France should provide us with a much easier case although it had three distinct monarchies during the nineteenth century before expiring in 1870. The House of Bourbon had ruled, interrupted only by the Revolution, from 1589 to 1830. The House of Orleans, a cadet branch, ruled until 1848 and the Bonapartist Emperors from 1800-15 and 1852-70. Succession in the first two cases was governed by the Salic Law, precluding the succession of female claimants or of a male claimant through the fame line. Descent of the Imperial title is governed by preferences expressed in the will of Napoleon I.
The male lines of Orleans and of Bonapartist have thrived and these two claimants can easily be identified. The difficulty lies with the Bourbon line in that the last three active Kings were all brothers. Of these, Louis XVI had two sons who both died in childhood, Louis XVIII had none and (d. 1836) Charles X’s elder son pre-deceased him, whilst his only legitimate male-line grandson Henri lived until 1883 and his other son Louis Antoine to 1844. Louis XIV’s male line descendants expired then as Henri died without issue and many of the Sun King’s other sons and grandsons died in infancy.
There is one loophole in that his grandson Phillip d’Anjou ascended the Spanish throne in 1700, as confirmed under the Treaty of Utrecht, by which he and his family renounced their rights to the French throne, a renunciation that Bourbon legitimists no longer recognise. However, the King of Spain and the hypothetical King of France are still not the same man because some of the former have disclaimed the French title. “Louis XX” is actually General Franco’s great-grandson.
The pedigreee is by “Bourbon-Wiki” by The original uploader was Muriel Gottrop at English Wikipedia – Transferred from en.wikipedia to Commons by RandomStringOfCharacters using CommonsHelper.. Licensed under CC BY-SA 1.0 via Commons – https://commons.wikimedia.org/wiki/File:Bourbon-Wiki.png#/media/File:Bourbon-Wiki.png