What happens to Wayne shortly after he receives Cal's (Toby's) letter in the novel, When Zachary Beaver Came to Town?

Wayne is in Vietnam. When Wayne writes a letter to Cal, he talks about Antler with great affection. However, both Cal and Toby cannot find anything romantic about their hometown. Cal often refuses to write Wayne back, not at an age where he likes to write letters. However, Toby believes he should and decides to write one himself and sign Cal's name. Wayne receives this letter shortly before he is killed in action.