there was this post where sullivan got old but was still doing his job and he went back to boo's door only to discover her all grown up with a baby girl.
She was. By the bad guy that wanted to put her the machine. She escapes him apparently. It is just not shown in the movie. Mike and sulky think it's their fault but then they realize it was the other monster's fault because he wanted to use the machine
I literally got up, walked around the room with my head in my hands, then sat down again. You dun good, OP.