Elemental items should stay degradable. If we would make them undegradable, the crystals will instantly crash in price. Killing tormented demons has become a decent money making method for mediocre players, so the drop in price would be devastating for them.
I do not agree on your idea about getting your crystal back, because similar problem occurs.
I am however suggesting an idea about elemental bow and staff, which currently have no use. First of all they need a slight buff, because currently dragon darts and god bows are better. Also I wouldn't mind seeing them undegradable, since they would still be used less than other items, also they don't deplete as fast as whips to (because of their usage). Currently using crystals on bows and staves is pointless. This idea does not expand to elemental whip.
I personally wouldn't mind if ancient items would be undegradable (they would still be untradable after being used), but there's a major problem in pvp. If a player dies wearing ancient gear, it currently becomes ancient energy. Since the items would be undegradable ancient energy is no longer used and it has no point (value drops to 0, pkers don't get loot from those items). Repairing ancient items is already very cheap and therefore I don't think it needs to be changed.