Firewatch is full of dialog choices throughout the game. How do my choices affect the story (or do they)? Is the ending the same regardless of what I choose? I've completed a play-through of it, and I'm wondering if it's worth going back to make different dialog decisions.
The ending will always have the same basic structure; when it's time you will
evacuate to Delilah's tower, she won't be there, and you'll have a final conversation with her about what you will both do next with your lives. You will never meet her.
Your choices throughout the game, and even at the end, impact the dialog and how your relationships grow and play out during the game. Some of them impact the makeup of your tower (which papers and such you have on the windows, what you are wearing, what pets you have, and the items you can opt to bring with you or leave behind at the end).
They don't, per se, lead to different endings (except one) where anything mechanically different happens. The one exception is
you can choose to not get on the helicopter, and it will eventually leave without you after a few minutes. But even this is not really that significant. You don't get any extra exposition or cutscene.