Describe several events from Ethan Frome that demonstrate the positive and negative aspects of the lack of communication.
For example: Ethan gets confronted by Zeena for shaving on a daily basis ever since Mattie's arrival.
Ethan Frome comments that people are saying Mattie is going to leave them, rather than telling her that Zeena is displeased with her work.
Ethan and Mattie's night alone together.
Jotham Powell refuses to stay for dinner - realizing that there is tension between Ethan, Mattie and Zeena.
The lack of communication is a major motif in the novel. Wharton explores it in terms of both literal physical communication and the more subtle aspects of emotional communication between and among the characters. The severe winter storms break communication among those of Starkfield and the outlying rural areas; people are isolated by geography and nature. When the primary characters are in each other's physical presence, however, they often talk without really communicating. Truth remains buried or unspoken; many conversations exist on two levels simultaneously--what is said and what is truly felt. One major theme developed in the novel is that isolation and loneliness, very destructive forces, result when people cannot communicate in meaningful ways, for whatever reason. As a result, it is difficult to find in the novel any positive aspects of the lack of communication.
In regard to the examples you have cited, the only positive results that might have accrued from them is that they served to temporarily avoid pain or conflict, to postpone it for a while. So long as the truth remained unspoken, life could continue without major emotional disruption. This, however, did not solve problems or eliminate the emotional conflicts that boiled under the surface. By avoiding their expression, they were deepened and magnified, leading directly to the novel's tragic conclusion. Had the characters communicated their feelings and thus acknowledged the truth, a "happy ending" might not have resulted in their lives, but the horrendous misery their lives became might have been avoided.
Finally, when Ethan raised the subject about Mattie's leaving them, he did so in the context of Mattie's possibly getting married. It was his way of dealing with that painful thought. Perhaps he wanted to hear her say that she would never marry, meaning that she would never leave him, even though he had no right to ask her to make that sacrifice.