This is how it goes. Let's say Wilma knew what Junko's plan was and how killing Mukuro wasn't part of the plan....a trap door was supposed to appear but Junko betrayed her. That made me think of this.... 

What would happen if Wilma got impaled by the spears instead of Mukuro?

This is how it would impact the Killing Game entirely. 

1. Monokuma breaks after seeing what happened which makes him release the spears immediately to see if she was okay....of course, she died after she fell to the ground with several holes in her body which makes him run off in panic

2. Everyone is devastated about what happened to her....but Mukuro was surprised at what she did to save her life 

3. The motives completely changed due to Monokuma's regret and guilt but he tries to hide it

4. The class trials are completely different and Mukuro gets to participate....but Monokuma sounds more somber and doesn't taunt the students

5. When it came to the mystery person who died....Junko reuses Wilma's body and tries to get rid of Naegi despite what happened

6. When he escaped execution, Monokuma doesn't get mad at him for breaking the rules....in fact, he was somewhat relieved 

7. When everyone figured out Mukuro's identity, she takes off the wig revealing her short black hair and when Junko reveals herself....she doesn't seem so proud of herself

8. After Junko's defeat, she falls into despair but not the good kind....she wanted to kill herself after what she did to Wilma....her eyes don't have spirals as she's close to hitting the button

9. Mukuro gets to live and the Future Foundation reverses the brainwashing effect her sister had on her

10. She tries to carry on Wilma's legacy knowing that she was supposedly going to be the new Headmaster after Jin's retirement