Regarding one who attains nirvana (a Buddha), there is no eternal soul or self but this does not annihilate the consciousness and provisional reality of a person who attains nirvana.
Iconodule, I didn't think about it yesterday, but isn't the consciousness one of the five skandhas?
The consciousness (vijñāna) that is one of the five skandhas manifests in six ways (as eye-consciousness, ear-consciousness, nose-consciousness, tongue-consciousness, body-consciousness, and mind-consciousness).
Both Theravāda and Mahāyāna would agree that when Siddhārtha realized nirvāṇa under the bodhi-tree, that Siddhārtha's skandhas, his body and mental structures, did not cease to exist. In Theravāda, this is 'nirvāṇa-with-remainder'.
I'm not not sure about the details of various Mahāyāna perspectives on the Buddha's post-death state, but in Theravāda, the death of the Buddha was his entrance into parinirvāṇa ('nirvāṇa-without-remainder'), where the Buddha was freed from being bound to body or mental structures. Parinirvāṇa means the cessation of all five skandhas, including all six types of consciousness (vijñāna): eye-consciousness, ear-consciousness, nose-consciousness, tongue-consciousness, body-consciousness, and mind-consciousness.
However, in Theravāda (and in Mahāyāna), parinirvāṇa is not a total annihilation of awareness or "consciousness" altogether. (If it were, parinirvāṇa would be no different than the lack of afterlife posited by materialists and physicalists). Awareness is still present, if only because there is "awareness" of parinirvāṇa. In Theravāda, this "awareness" is known as citta, or the heart. When the citta is purified of ignorance, nirvāṇa (freedom from bondage) is realized. When the citta is contaminated by ignorance, craving arises, producing bondage.
Some have argued that the Mahāyāna or Yogācāra idea of ālaya-vijñāna corresponds to the Theravāda citta.
Some may argue that this purified citta is the "true self", the "atman", but a Theravādin would argue that words like "self" and "atman" simply encourage the self-grasping, craving, and ignorance that produce further dissatisfaction, suffering, and bondage.