Chris Kent was flushed
Tim's history still is in the trash even in Rebirth when they gave him a modified version of his origin back DC still disposed of any possibility of his Robin past coming back by de aging him.
Kon is a work in progress. He wasn't chopped and stitched as much as Tim so it's easy restore him
Damian as problematic as he makes Batman universe mythos has retained all his history.
In my opinion None of the above are essential.
In my opinion Dick and Jason are the only two robins essential to the Batman story but I don't get to decide.