Remember, this last episode they spoke of the reaping and how it occured. It sounded like they believed in it as well. But, here is the deal, that I think "may" just be going on. I made a partial guess about this before, but now there is more proof.
I really DO think Sophie's sister (the witch that died) IS in fact going to be reborn into Klaus's unborn child. The reaping sounds A LOT like witches "killing" someone, but keeping their souls hanging around (sort of like the same thing with how they must bury the dead within a certain extent of time to keep their ancestral links connected), then a bit later during a one day period that soul is then moved into an about to be living fetus (or something like that, for all I know they may actually snuff out the life of someone else to do this...like a non-death abortion if you catch my drift).
In Klaus's case though, he REALLY was going to have a hybrid baby. But these idiotic witches have now created a BIG ass trench from which they are about to enter and can't leave. THIS is where the warning came from (and why all witches will suffer as well). IF Sophie's sister put herself into the baby somehow and will be reborn, she will NOT be reborn as a wtch--these powers will get CUT-OFF. No vampire has access to these things...
So if ancestral magic is their complete link and the reaping takes place (and quite possibly, Sophie's sister may have put herself into the running for it, not fully understanding what the sacrifcial rebirth spell really did and what its implications were) or doesn't, once the child is born Sophie's sister's link into the ancestry via that spell will undo ALL of it.
But, this is a partial theory in motion. That being said, parts of this theory may still be true while others are not (like Sophie's sister putting herself in the hybrid baby's body, etcetera; which may explain the "direct damage" link Sophie has with Hayely, because it is force feed through the ancestral magic line with Sophie's sister...if that makes sense). Anyway, take what you like and don't like.