We analyze the effect of finite ion Pedersen mobility on the evolution of ionospheric barium clouds. We find that the Pedersen mobility provides a mechanism whereby barium can leak out of the region of elevated magnetic-field-line-integrated electron density/Pedersen conductivity and hence lose the ability to structure further. The essence of the mechanism is that the finite Pedersen mobility of the barium ions allows them to separate from the cloud electrons, which have virtually no Pedersen mobility. The barium is replaced in the electron cloud by the ions constituting the ambient ionosphere, which are compressed up to the required densities by their own Pedersen mobility. (Here we take the ''electron cloud'' to be that defined by regions of enhanced magnetic-field-line-integrated electron density, not by local electron density enhancements.) In the process of exiting the electron cloud the barium is expanded and hence attains a density lower than when it coexisted with the electron cloud. For many ionospheric parameters the barium will have in effect left the region of further structuring, which will still be proceeding in the electron cloud. As the barium leaves the electron cloud it can form a long thin sheet of lower-density barium one side of which is considerably steeper than the other, which extends from the leading (nonstructuring) edge of the cloud. An observer watching only the barium or only local electron densities would conclude that the structuring process had ceased. Further, the electron cloud itself may decay if the ions coexisting with it are subject to a fast recombination chemistry.