The tectonic mask 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 mask 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 mask had 52% of its charges remaining, 7 tectonic energy would be dropped on death. This can be used to refund most of the cost of the mask, although the stones of binding are not returned.