The tectonic robe bottom lasts for 100,000 charges of combat before degrading to nothing - it cannot be repaired. Once equipped, it instantly becomes untradeable, even if it has not been used in combat.
Losing the tectonic robe bottom by being killed in the Wilderness will result in a fraction of the original tectonic energy being dropped on death, based on how degraded it was, rounded down. For example, if the robe bottom had 52% of its charges remaining, 14 tectonic energy would be dropped on death. This can be used to refund most of the cost of the robe, although the stones of binding are not returned.