Thank you so much for checking the game out, I'm so so honored that you enjoy it!!
The game will automatically reset once you see ending 1, but it still will remember all the posters you collected even if everything else are set to the beginning- so while yes you still have to go through some puzzles and dialogues in order for you to get to the point where you could get any endings you missed the game will know all the deaths/endings you've seen so far (even if you didn't see them in this new run)! So you can just see the any endings you missed. Hope this was helpful!!