Today, I had Saharah, the carpet-selling camel, in my town. Since this was only my first day playing, I couldn't buy any carpet from her as she would not sell me carpeting for my tent.
Some of my friends, upon hearing that she was visiting my town today, decided to take advantage of her random appearances by heading over to my town to peruse her carpet styles. Unfortunately for them, when they arrived in my town Saharah was nowhere to be found. Assuming she left, my friends left my quiet little town to return to their own. I didn't have Saharah anymore, why would they want to stick around?
However, once they left, I saw Saharah again. She was just wandering aimlessly around my town.
Does she, or any other special NPC, leave when friends visit?