I'm not aware of any events or glitches that would cause the behaviour described by
@blackbirdgriffi - the glitch he described may well be real but, if it is, I think it's very uncommon.
AFAIK, there are only two ways to preserve your bloodline: console/modding; and having another child. Since you're not wiling to do the former, I won't go into that. Since you're immortal, there is a way to have a child: become grandmaster of the satanists, be matri-married to someone (so the child isn't a bastard) and use unholy impregnation on yourself. (Unholy impregnation is permitted for women who are under 45 or immortal.)
Additional notes:
--- If you matri-marry a man with multiple bloodlines, your demon spawn will get his bloodlines as well as yours.
--- Take a save (and or, if in ironman, a backup) before the unholy impregnation - in case your husband discovers he's been cuckolded by a demon.
--- Be warned that a demon spawn will try to kill your other children. But you implied they're all dead, so I guess that's not a big deal. I don't know what happens if you do unholy impregnation more than once - do they kill each other until only one remains? Or do they tolerate each other?
EDIT: Some more notes:
--- The demon spawn becomes immediate grandmaster of the satanists on turning 16. I'm not sure how this works if he is not controlled by the player, or if the player is already grandmaster.
--- Playing as the demon spawn can be pretty entertaining (and it's a way to ensure he/she has many many kids)... but you'll need to die/abdicate. Or set him up as a crusader beneficiary?