User blog comment:Xilinoc/Ch. 579 - THE UNDEAD 6/@comment-24913480-20140507201544/@comment-11051098-20140507204639

It was said that the piece of his soul that Yhwach gave to another person, will return when that person dies. As far as I recall, it was never stated that their power goes to Yhwach together with the soul piece. Unless their power becomes a part of their soul and both "fuses" with Yhwach's soul piece, I don't see the whole thing happening.

If it does, with every Sternritter, Yhwach will eventually become way more ridiculously overpowered than Hôgyoky-Aizen and post-Dangai-Ichigo ever were.