As for the first question, we can regard Shi`ism as a natural consequence of Islam, and as a representation of the presentation of Islam which it was obliged to attain if it was to protect its healthy growth.
We can in fact infer a logical inference to this presentation of Islam from the faith which the Prophet commanded, according to the nature of its formation and the conditions which surrounded it. The Prophet was assuming the leadership of a revolutionary faith, and inducing radical transformations of the customs, structures and concepts of society. The path for such a task of transformation was obviously not a short one, but was rather long and protracted because of the vast spiritual divisions between jahiliyya and Islam. The faith which the Prophet practiced had to begin with the jahili man and raise him to new institutions, thus converting him into an Islamic man who could carry the new light, and uproot the trunk and roots of jahiliyyah from his heart and mind.
And the Great Leader made astonishing headway in the task of transformation in a very short time, but it was necessary for this task of transformation to continue on its way even after the death of the Prophet, who knew that his death was near some time before it actually occurred and he disclosed this openly in `The Pilgrimage of Farewell' (Hajjat al-Wada); so his death was not unexpected.
This means that he had ample time to contemplate the future of the faith after his demise, even if we disregard the factors of contact with the Unseen and the divine protection for Islam stemming from revelation. In light of this we can see that the Prophet had three possible paths before him to ensure the
proper consequences of the future of the faith.