Board Thread:Lore Discussion/@comment-86.24.50.100-20130623082136/@comment-10993011-20140825170233

I think we can assume there are plenty of Septim heirs, just no direct heirs. Considering most of the Emperors were Bretons (except for Tiber Septim himself) up until Cephorus II (he himself was not a direct heir), we can assume they intermarried with the nobility of High Rock and families with Septim blood could still be there. We know they were in Solitude (hell, Toryg could have been a descendant of Cephorus II or Jolethe Direnni, the sister of Pelagius the Mad), and they were in Silvenar in Valenwood (Kintyra I was a queen of Silvenar).

But is the Dragonborn a Septim descendant? No, but the Dragonborn is Dragonborn and thus could still potentially rule Tamriel, though I'm sure Bethesda won't make that happen.

Also, if we're still on the subject of Mankar Camoran, if the amulet fits he may very well been of Septim Blood. Though this is just speculation and fan theory, he could have a descendant of Kintyra I, who was queen of Silvenar and likely married a Bosmer noble. For all we know, a male sibling of Uriel Septim I married a Bosmer woman who in turn gave birth to Camoran Usurper who had Mankar Camoran as a son.