Mika's doppleganger disappeared as Dean found the real her, leaving absolutely no trace of her ever being there. 

Mika caught a glimpse of Dean running toward her and the spirit as she flew over the wall and went underwater. She hated being thrown underwater on cases and she wished she could do a case where she was nowhere near water. She was unaware that Dean managed to fight off the spirit, even briefly for the time being before throwing himself in the water after her. She had drifted in the spring down to the back and into a corner, where she fought to get up to the surface but her foot got caught. 

Struggling to get free she pulled and yanked as hard she could on her ankle to free herself, wondering what she could have been caught on when in theory it should have been a smooth floor underneath her. She was going blurry eyed as she knew she was running out of oxygen but she could hear very faintly Dean screaming for her. 

Suddenly her foot got clear and that's when she saw a grate in the floor but beside said grate she saw remains. With the last of her breath, she grabbed what she could and made a beeline for the surface. "DEAN! I FOUND HER REMAINS!" She shouted, starting her swim over to where his voice was coming from. "WHERE ARE YOU!?" She shouted out, needing to know what direction to even go towards, being under water for as long as she had been had completely made her disorientated. 

The spirit came back and went for Dean once more, not wanting them to be near her remains she threw Dean out of the spring and onto the ground.