AKA the 'Death of God' movement. Theothanatology is a religious position that holds that Nietzsche was right -- God is dead. And dead in just the way that Nietzsche meant; we have lost God, and E no longer has a meaningful role in our lives. However, theothanatology tends to be a position held by members of the Christian church who believe that the death of God is both figurative and reversible, and that reinvention (or reconceptualization) of God is both possible and necessary.
The Death of God movement started in the 1960s, when a number of Christian theologians took Nietzsche's idea that God is Dead and decided that it was 1) true and 2) a good way to get people thinking seriously about the role of God in their life. Gabriel Vahanian's 1961 book The Death of God started things off by claiming that today's society was too secular, and had no place for an abstract, transcendental God. Various theologians have suggested that the modern skeptic will be able to find God -- the true and real God -- in various places, for example, Jesus (a concrete and real person doing God's work), or embodied in the actions of communities of faith.
Theothanatologists, in other words, do not believe that God is dead, but only that we have lost him. Which is really no different from what any religious leader says to the non-believers.
The term theothanatology is constructed from the Greek words theos, meaning 'God' and thanatos, meaning 'death'.