The last thing we see on stage in Arcadia is two couples, one from the present and one from the past, waltzing into the future. What else is there to do when the world is doomed? That may seem a bit flippant, but Arcadia encourages us to take that question seriously – if "the future is disorder" (1.4) as Valentine says, if humanity is going to die out and all human works disappear, what's the point of doing anything at all? The waltz at the end of Arcadia offers a protest against the notion that knowing that we're doomed means we should all sit around in the dark whining: even if, like Septimus, we can't "save the world through good English algebra" (2.7), perhaps having fun is itself meaningful.
While "fight the end of the world – have a dance party" might make a good bumper sticker, the conclusion of Arcadia also challenges the very notion of ending anything. After all, the night of waltzing happens in the middle of Thomasina and Septimus's story. We know that Thomasina is going to die, and Septimus is going to become a hermit. Ending the play in the middle of the action forces us to think about storytelling order. Defining a clear beginning, middle, and end to a story helps us to make sense out of chaos, but even so, the play reminds us that beginnings and endings can be just as arbitrary as the steps of a waltz.