Does Sword of Feast and Famine untap your lands if the equipped creature deals combat damage to a player with protection from green?

Sword of Feast and Famine reads: "Whenever equipped creature deals combat damage to a player, untap all lands you control." This is a triggered ability that requires combat damage to actually be dealt to a player as its condition.

Protection from green (granted by the Sword itself, among other sources) has four components summarized by the acronym DEBT: the protected permanent or player cannot be Damaged, Enchanted/Equipped, Blocked, or Targeted by green sources (CR 702.16b). The damage prevention aspect means that all damage that a green source would deal to a player or permanent with protection from green is prevented (CR 702.16d).

Because the Sword is a green artifact, any damage the equipped creature would deal to a player who has protection from green is fully prevented before it is ever "dealt" (CR 702.16d, 615.5). Since zero damage is dealt, the trigger condition on Sword of Feast and Famine is never met, and the untap ability does not trigger at all.

Example: Your Mirran Crusader (which has protection from green) is equipped with Sword of Feast and Famine. You attack your opponent who somehow has protection from green (say, via Leyline of Sanctity styled effect granting it). The Sword is a green source, so all combat damage it causes to be dealt to that player is prevented. The trigger never fires, your lands stay tapped, and your opponent discards nothing.

Note that if the player does not have protection from green, the damage goes through normally and both the untap-lands and discard triggers do fire (CR 603.2).