Hi, just played this game and we weren't sure when to stop.
We ended the game with maybe 8 needles still on the board, but they were all individual needles on a single tile, we didn't think it was useful to move one meeplebone space over, when it couldn't do anything besides move around.
When is the end?
FYI, a move cannot end on an empty space! Moreover, you must drop your last meeple on a space with at least one other meeple of the same color (which is why it cannot be empty).