As far I remember. . .
Sophitia destroyed one pierce of the sword in Soul Blade (the female version [!] of the sword). Raphael was the first character who completely destroyed the sword in Soul Calibur II - that's when Siegfried and Nightmare got separated (Raphael Vs Nightmare is also the true destined battle in the game). Nobody destroyed it in Soul Calibur 3 and I don't know about Soul Calibur IV - I believe Sieg destroyed it, but I'm not 100% sure. And I guess we can consider Patroklos and Pyrrha the ones who destroyed Soul Edge in Soul Calibur V.
Seigfried in SCIV destroyed Nightmare/Inferno, but he didn't destroy the sword. That's what I saw in the intro. I may be wrong about that.
Patroklos and Pyrrha destroyed both swords, which was a rushed idea, once again.
The next game (SCVI) should be leading towards their resurrections (or maybe Soul Edge's itself), and then the next few games is slowly leading to the end.
Another idea for SCVII is to have only Soul Edge remain active and characters desperately try find Soul Calibur since that was destroyed, thanks to the Alexandra siblings. Without Soul Calibur, there is no use of destroying Soul Edge.
Of course the SCVI idea can be difficult to do since the swords are the actual protagonist/antagonist of the game's story, but with some thought it won't be too bad. They already have evil/malfested characters from both sides of the world. They need to use that to their advantage. It would be nice to wonder about Voldo's state without Soul Edge around. Does he just sit there, or does he try to find "evil" characters?
Pyrrha becoming Pyrrha Omega again won't be so hard. She just has to fight people, and Tira will try to find her to do it.
If Raphael is Graf Dumas, then the plot idea for Nightmare, ZWEI, and Viola is still active too. Players still do not know about ZWEI and Viola's origins yet.
PS has HUGE potential with the Asian group. Xiba, Natsu, and Leixia especially. I just gave them ideas on that part.