Reaction

Wilson- Wilson is devastated. He always thought he didn't deserve Mertyl. Through her death, he discovers her infidelity except he targets the wrong person (Gatsby). 

Tom- Tom might have loved Mertyl in his own patriarchal rich man way. Tom however is a hedonist and moves on.

Nick- I don't think Nick is especially affected. He did not know Mertyl for very long and was not impressed with her. She was having an affair with Tom thus betraying Nick's cousin Daisy.

Gatsby- Gatsby was not really interested in Mertyl. Unfortunately the consequences of her death directly affected him.