@Edgar Allan Pillow
This might explain why some shards are 'killed' while Ruin and Preservation despite being killed, it was possible to merge them and so now they are hold from Sazed.
The Shards of Dominion and Devotion were Splintered and trapped in the Cognitive Realm by Odium. While the power of most other Shards resides in the Spiritual Realm, Odium has locked the power of Dominion and Devotion in the Cognitive Realm to ensure that nobody on Sel could gain those Shards. This makes the Cognitive Realm on Sel extremely dangerous as anyone who comes there unprepared would be ripped apart by the power of the Shards, now collectively known as the Dor.
Examples of Splinters are Honorspren (Splinters of Honor), the Unmade (Splinters of Odium), the Divine Breath that Returned hold (Splinters of Endowment), and the Aons inside of Seons (Splinters of Devotion)
This might explain why some shards are 'killed' while Ruin and Preservation despite being killed, it was possible to merge them and so now they are hold from Sazed.