The sirenic chaps lasts for 100,000 charges of combat before degrading to nothing - it cannot be repaired. Once equipped, they instantly become untradeable, even if they have not been used in combat.
Losing the sirenic chaps by being killed in the Wilderness will result in a fraction of the original sirenic scales being dropped on death, based on how degraded they were, rounded down. For example, if the chaps had 52% of their charges remaining, 14 sirenic scales would be dropped on death. This can be used to refund most of the cost of the chaps, although the algarum thread is not returned.