HERE IS WHAT SHOULD'VE HAPPENED:
The students leave to go to Seoul to reunite with their parents. On their way they find the group that were heading to Seoul killed and that cements their idea that is best for all of them to remain together. They come across an amusement park and turn their dreary journey into an opportunity to enjoy themselves because they are uncertain of how the future will be. Footage of Su Cheol's death is found, and the others watch it. Yeong Soo is tripping balls after the cancellation of the CSATs and comes across So Yeon. He attacks her as she tries to fend him off and is knocked out. Il Ha comes across Yeong Soo kissing So Yeon and beats him up. During the fight a gun goes off and Il Ha is injured. Thinking that Il Ha is dead Yeong Soo tries to cover it up. Yeong Soo is found by the others who rushed to the area after hearing the shot. Yeong Soo is tied up and the students leave the area as spheres are drawing near. The group carries an unconscious Il Ha and a tied-up Yeong Soo to a nearby school to take refuge. Yeong Soo is paranoid that Il Ha will wake and tattle and manages to escape his ties and in his poor mental state conjures phantom spheres that he must defeat to earn more credits for college. He mistakes the other students and kills a few of them before they manage to stop him. The noise of the gunshots attracts more spheres and the injured and uninjured fight their way out losing more students in the process. Il Ha and his friend die in the fight to escape. The ones that survive eventually manage to find a way onto an abandoned outpost after the escape. Later the govt announces a new weapon and the alien threat is neutralized, and the word starts to rebuild. There is a memorial at the school to honor the students that were drafted in the military and didn't survive. A plaque with each of the fallen were at the base of the memorial to honor their sacrifice and bravery.

I thought the sudden death of so many of the students too abrupt and a poor ending for their growth, sacrifices, and struggles. So, I made an ending that was more honorable and didn't piss on the hardships that they endured and the on the people that they lost on the way while retaining the core of this poor episode.
This season overall was okay, and I would've been fine with it, but the end scenes were too much to justify that ending. To me it betrayed the previous episodes, including the previous season. It made all that happened a joke, basically pointless, a waste of time. I've seen people justify that there was a reason to his madness, and it was a fitting ending. But it could've been written better. Il Ha should have a heroic ending protecting a friend from the spheres. It would have fit more since people died because he was afraid. If Yeong Soo had is final break it didn't have to be a near complete massacre. I enjoyed the previous episodes before the last. I was just disappointed on how abrupt it was.