It looks like the creators of Baldur's Gate 3 have taken care of all the possible situations that could block the main quest line. A player with the nickname Proxy Gate Tactician tried all the ways to lose an artifact important to the plot and discovered a lot of new content.
In the third act, the main character will have all three Netherian stones from the crown of Karsus in his hands, which will allow him to curb the Elder Brain in the finale of Baldur's Gate 3. It would seem that it would be worth losing three small stones, but no: the developers have provided for almost all situations in which the player can «sow» an artifact.
Proxy Gate Tactician was convinced of this from personal experience. In his video, he tried all available ways to get rid of stones. To his surprise, Larian Studios got creative with their return. In one of the situations, the player will be helped by... a fish.
So, you can try to leave stones in the Iron Throne underwater prison, which self-destructs in any outcome. In this case, the artifact will end up with one of the merchants. But even if you kill him before visiting the Iron Throne, the stones will not be lost: they can be found in a fish on the coast of Baldur's Gate, which swallowed them after the prison explosion.
Another unique encounter occurs if you lose Netherian stones in the Steel Watch Foundry. In this case, it will be possible to find marauding kobolds in the game world, and the artifact will be found in their inventory. You can see all the situations in the video below:
As Proxy Gate Tactician himself admitted, he saw many of these situations for the first time in 1400 hours of play. It is possible that some of the content was added with updates.
Earlier, details of a future major patch for Baldur's Gate 3 appeared. And before that, it became known that Larian Studios could release new parts of Fallout and Ultima.