Melissa and Ashley didn't really run away. They just left that area of the mall, so that they could sneak back and steal that gun without anyone noticing.
When they came back, they hid behind some of the decorative plants that surrounded the food court. They watched as the geek freaks talked to each other and finished their food. Melissa found Biff to be very dorky looking now and kind of felt sorry for him, that he'd have to remain that way until someone (like her) changed him back to normal. If she didn't, he'd be that was for the rest of his life.
As they watched, the geek girls decided to use the restroom, leaving only Jay, Jon, and Biff at the table.
"Well, that makes things easier," Melissa whispered to Ashley.
"You want me to stall them?" Ashley asked.
"Sure. It'll definitely help."
Ashley moved around the food court, so that the three geek freaks wouldn't notice her, and entered the women's restroom that she saw the four geek girls enter just seconds before.
Meanwhile, Melissa still hid behind the plants, waiting for a chance to steal that gun.
