UPDATE: Okay, after a solid week of looking for the Play-doh all over the house, on Sunday, when the little girls were over again, I quizzed them -- gently -- about the location.
They had no clue.
However, while replacing a toy on the toy shelf, I happened to move what I thought was an empty Boy Scout popcorn tin. The tin felt heavy. As it should. Because THE PLAY-DOH WAS INSIDE IT.
One of the girls had taken the empty tin off the table last week and used it for Play-doh storage. And didn't tell me.
The good thing? The Play-doh was still pliable! They played with it, again.
But this time, I know where it's at.