No. There need not always be yin(g) and yang.
In Buddhism, they describe something called the "paramitas" or "perfections." These are the one-sided (non-dichotomous) forms of things like generosity, confidence, compassion and wisdom. They are not tainted with their earthly opposites.
We find similar ideas in Christianity, with ego (false self) and the true self (soul, Holy Ghost, child of God). Ego is the self that must die before one can realize the "everlasting life" of which Jesus spoke. Once ego is gone, one returns to the paramita ("other shore") of existence, where yin and yang no longer exist.