edit--As corrected below, I mean Sophie's niece, Monique, not her sister. So I'm replacing "sister" with "niece", to make my post far more understandable.
This last episode we saw that Sophie got her niece back (of course we HOPE that this is indeed what happened; as a situation could be occurring much like Celeste occupying other people's bodies and that somebody has "hijacked" Sophie's niece's body...as it was fishy that she talked to Celeste as soon as she awoke, but they may have just been coincidence--although since I'm editing this I may as well add they we know that Monique is more than likely working to some degree under false pretenses for Celeste, as Davina was forcibly ostracizing while with her ancestors).
If she really did come back it may be true that for the NEW gang on The Originals to get Davina back they will need to kill all of the four witches that have been brought back to life by Celeste (most likely Celeste too, but we will see--Celeste may even be "stubborn" about allowing Davina back, since she betrayed her "coven" in a way...so she may try to deny her of her resurrection or give her a punishment of some kind). As they kill each witch, a new girl will wake up in her tomb, alive.
I'm unsure of in what order the girls were killed or even what order they will come back in. But, if Sophie's niece was the first to go, then we also know who will be resurrected when the witches die, one-by-one. This may also lead to a witch-on-witch war, if other witches like Sophie and her niece (as she seems fairly sharp concerning magic) understand the mechanics fast enough and can see what I'm saying is completely true (though others may see it first too)...
It'll be interesting to see though. The Originals is showing that it can be a very good TVD alternative.