At the end of Chapter 7, Nick observes Gatsby, Tom, and Daisy after the accident. What conclusions does he reach?

After all of the chaos created in Chapter 7, climaxing with the accident that kills Myrtle, the end of Chapter 7 is quite calm.  Nick discovers Gatsby standing outside of the Buchanan house; Gatsby tells Nick, "'I’m just going to wait here and see if he tries to bother her about that unpleasantness this afternoon. She’s locked herself into her room, and if he tries any brutality she’s going to turn the light out and...

After all of the chaos created in Chapter 7, climaxing with the accident that kills Myrtle, the end of Chapter 7 is quite calm.  Nick discovers Gatsby standing outside of the Buchanan house; Gatsby tells Nick, "'I’m just going to wait here and see if he tries to bother her about that unpleasantness this afternoon. She’s locked herself into her room, and if he tries any brutality she’s going to turn the light out and on again.'"  And while Nick originally does not think that Tom would ever harm Daisy more than the mental abuse of cheating on her, he has a moment of doubt, so he decides to look in on them and report back to Gatsby.  What he sees tells him that Gatsby is "watching over nothing": 

Daisy and Tom were sitting opposite each other at the kitchen table, with a plate of cold fried chicken between them, and two bottles of ale. He was talking intently across the table at her, and in his earnestness his hand had fallen upon and covered her own. Once in a while she looked up at him and nodded in agreement.

They weren’t happy, and neither of them had touched the chicken or the ale — and yet they weren’t unhappy either. There was an unmistakable air of natural intimacy about the picture, and anybody would have said that they were conspiring together.

That last line is especially telling, as Nick can see that Tom and Daisy are in this together.  It does not matter that Daisy was driving; they are going to lay the blame on Gatsby and move on, leading Nick to conclude at the end of Chapter 9: "they smashed up things and creatures and then retreated back into their money or their vast carelessness, or whatever it was that kept them together, and let other people clean up the mess they had made. . . ."  In a way, Daisy and Tom are perfect for each other.

For Gatsby, he is left dead, with not even the whisp of the dream.