Change is never easy. Due to that, I think the more likely outcome is to keep the schools separate. As you said, both schools have also been renovated recently. Eisenhower did major improvements around 2014-15 and Mac just in the last year or two.
The only way I see this happening is if enrollment continues to decline substantially. If Ike and Mac (combined) fell to around 1,500-1,600 students, a single high school, even if both campuses were still open and utilized, would have enrollment close to Chatham or Springfield. 6A for football and 3A for hoops.
Decatur had 4 public high schools in the early 1980's. Lakeview closed in 1982, and Stephen Decatur closed in 2000.