Susan Beth,
That raises the question of what else they *could* have done with Cally. Ideally, she could have become Blake's successor in the sense of promoting pro-rebellion actions. It would have flipped the dynamics of the first season a bit: we'd still have had the pragmatist vs. the idealist, but it would have been the pragmatist who held the power position.
Somehow I think Cally would have been better as persuading the others to join her in ganging up on their leader and overruling him on occasion than Avon ever was. :-)
Your suggestion of Cally being Blake's successor as leader is very good, and a nice subject for anyone writing fanfiction.
Murray