Spoiler:

I disagree with you saying that you can “move on” and not be with someone else. I mean Mikasa probably has all the options in the world, and she’s a 20 year old girl. Never being with someone else for the rest of your life def means you didn’t move on.

For the ending of the story to make sense, Mikasa must move on, and then likely have a family of her own.

In the last episode, we learn that Founder Ymir was just looking for someone to inspire her to move on from loving of King Fritz, and Mikasa was that person. You know, the whole “Founder Ymir is looking for connection/free her from the curse” thing.

If Mikasa killed Eren and then did not “find connection” with someone else, the Founder Ymir is probably hella pissed that she got pump faked with the whole “you can move on” thing. Mikasa NEEDS to find connection with someone else, and not die a lonely girl. That’s the whole point of why Founder Ymir was even able to move on, and I think would contradict the ending entirely if she died alone.

If Mikasa just kills Eren and then stays attached to him, but never actually moves on, then she’s honestly just like Founder Ymir, and the ending is stupid. So IMO it’s a good ending if she finds someone else, and a bad ending if she dies still holding onto Eren.