The tone of the last paragraph is 'solitary'.

'Sometimes also a man or woman much older falls silent for a day or two, and then leaves home.'
When I think of home, I usually think of people who share, eat, and live together. But, the quotation above says that 'a' man or woman 'leaves home.' This shows how independent the people are, and puts an emphasis on the 'solitary' tone of the last paragraph.

'Each one goes alone, youth or girl, man or woman.'
This phrase shows how ultimately people are alone. Some might stay for their own reasons, but some leave independently because of their own reasons. There is no togetherness in this last paragraph.

'Night falls; the traveler must pass down village streets, between the houses with yellow-lit windows, and on out into the darkness of the fields.'
This phrase also emphasizes the 'solitary' tone because it talks about a single traveler alone in the night and darkness. The image of the traveler traveling alone in the dark shows how people live on according to what is best for them.

'They leave Omelas, they walk ahead into the darkness, and they do not come back.'
The words “leave” and “darkness” both contribute to the solitary tone of this sentence as well as the entire paragraph. I usually correlate darkness with isolation and abandonment because almost everyone fears darkness and even if we have someone else around, darkness makes us feel as if we are all by ourselves because we cannot see anything. Since we cannot see anything, darkness also relates to loss or inability to determine any direction; therefore, I made a connection between darkness and desertion. The phrase “they do not come back” adds to the deserted feeling this particular sentence is giving to the readers.

'But they seem to know where they are going, the ones who walk away from Omelas.'
Just like the sentence above, those “who walk away from Omelas” leave things behind as they move to somewhere else, emphasizing the remote, lonesome mood of the concluding paragraph although the end is quite forward-looking and positive because they seem confident “to know where they are going”. Nevertheless, walking away from a place is tinged with loneliness.