A Crimson Stalker’s Heart is their weak-point, it’s exposed due to their lack of flesh protecting it, however, reaching it without being absorbed into their bodies, and past their ribs can still be tricky.
Once their heart is pierced, or injured enough to stop it from beating, the heart starts to turn grey and crumbles away to a cloud of dust. Their bodies slowly disappear like smoke, leaving only their Crysalis shards and their dark crimson bones scattered where they once stood.
This is the only way to destroy them, and as far as the Valkte know - there is no way of curing their blood lust to revert them back into the Valkte they once were.
However - once a Crimsons Stalker is slain, the Valkte's soul is released from the Crimson cage moves on peacefully. In a sense - it's a mercy to slay them to release the Valkte's tortured soul trapped in it's Crimsons wisps.