When you switch to the “Browse map data” layer in the edit menu at osm.org or load that area in an Editor like Josm or Merkaartor or open potlatch2 editor for that area, you can see that the single points (called nodes) of the border still exist!
It seems that the border way itself has been “removed” by the Redaction Bot … so if you are able to, remap the border line with any editor you want.