We've already seen a couple of times now that the Master Sword in Breath of the Wild isn't exactly in its best shape anymore. It almost looks broken. And this raises the question, if there's actually a limit to the Master Sword in this game, similar to the Razor Sword in Majora's Mask.
Of course it wouldn't be lost forever, if it breaks, but you'd have some expert blacksmith repair the thing for you or something similar. And naturally you might bring it back to its former glory during the course of the story. But why would Nintendo limit the Master Sword like this? One word: Adventure Pouch.
The Adventure Pouch was a new concept in Skyward Sword that got now heavily extended in Breath of the Wild. It not only holds shields, ammo and potions, it pretty much holds your entire equipment. Skyward Sword also introduced durability to shields, where they could break, but where the shields also came with different advantages and you had to bring the right tools for the job. This system now applies to the majority of Link's items:
- Melee Weapons
- Bows and Arrows
(Not sure, if Armors have durability as well.)
One problem with the shield durability in Skyward Sword was the Hylian Shield. It couldn't break and essentially replaced all other shields in the game. It made them obsolete. But it also wasn't available until very late in the game, where it then felt like a huge reward... Something similar might apply to the Master Sword in Breath of the Wild, but probably not before it was fully restored. In its decayed state you might not be able to use it infinitely.
I personally do like this whole system of weapons, bows, arrows, shields, armors and even horses as resources, where you have to make strategic decisions of what to bring with you. It adds a new layer to the gameplay of Zelda. However, I worry that in the end of the game it all won't matter anymore, because Link simply runs around equipped with the traditional indestructible Hero's Clothes, the Master Sword, the Hylian Shield, the Hero's Bow and even Epona, making everything else in the game obsolete. It would be boring and also kind of give the wrong message, where the old stuff is still the best and the new Adventure Pouch system was just a hindrance, instead of an interesting gameplay mechanic.