In Neuroshima Hex 3.0 a player starts their turn by drawing up to three tiles and discarding one of them into the discard pile. Are these tiles out of the game permanently or is the discard pile essentially just your supply of tiles? In other words, when I discard a tile will I have the chance to draw it again or not?
Discarded tiles are out for the remainder of the game. While the rules don't specify this, they never allow for reshuffling of the draw pile. This would also force you to maintain separate discards for your defeated tiles and your discarded-from-hand tiles, which is an unnecessary and unspecified complication.
As further proof, the behavior in the Neuroshima Hex 3.0 mobile game is that discarded tiles are, simply, discarded (permanently).
I'm sorry that I don't have anything more official to cite here, but I believe that both the behavior of the official app and nature of the rules stated are sufficient as proof that discarded tiles are truly discarded.