Do Beings go into total unconsciousness before attaining Buddhahood?

In mahayana I believe that at least some practitioners have claimed that -- like the Buddha himself -- one attains enlightenment after the formless meditations. That means you don't perceive what you see, taste, smell etc., though I'm not sure if that means you lose consciousness of them.

The fomrless realms / meditations are pretty crazy and very unusual. I mean the 8th is called "neither perception nor non-perception", but not because it is enlightenment.

You could be asking about nirodah samapatti, but few claim to have attained it.

https://en.wikipedia.org/wiki/Dhy%C4%81na_in_Buddhism#Nirodha-sam%C4%81patti

Is it death?

There's a nice paper on the topic, called "Why the Buddha Never Uttered a Word" by Mario D’Amato - you can find it on Academia website.

You'd do best to read it all, although you may certainly prefer to skip to a section titled "Mindful Buddha versus Mindless Buddha".

There Mario cites some other work that says:

... Dunne goes on to specify that according to Candrakīrti’s account of buddhahood, for buddhas “the fluctuations of mind and mental functions” have “completely ceased”. Jayānanda (c. 1100), the only known Indian commentator on any of Candrakīrti’s works, affirms Candrakīrti’s account and “explains that enlightenment is a process of ‘not knowing’ and is characterized by the elimination of the knowing instrument, the mind”.

…

Dunne states that, according to Candrakīrti, “the dharmakāya causes a didactic sound to emit from a buddha... [but] the production of this sound does not at all mean that a buddha is cognitively active”. Being mindless, a buddha is unable to use language in any ordinary sense; on this view, a buddha only appears to use language—what is actually occurring is that certain sounds emanating from a buddha are interpreted by unenlightened beings as words and language.

Mario then goes on to argue that, in his understanding,

... it is only metaphorically the case that buddhas do not use language. On the model of the awarenesses of a buddha considered here, a buddha possesses both a nonconceptual and a conceptual awareness, and it is a buddha’s possession of some form of conceptual awareness that allows for the use of words and language. However, through the attainment of nonconceptual awareness—through directly apprehending thusness, the fundamental, ineffable nature of things—a buddha’s relation to conceptualization and language has been radically altered. In any occurrence of language use, a buddha would remain aware that putative linguistic referents do not actually exist. A buddha would employ language without falling under the spell of words and objects—employing concepts and language in perfect accordance with conventional usage, while remaining aware that ultimately there are no referential objects. We might describe a buddha’s mindful awareness in terms of what some contemporary philosophers have referred to as fictionalism.

Stanley states: “On a fictionalist view, engaging in discourse that involves apparent reference to a realm of problematic entities is best viewed as engaging in a pretense. Although in reality, the problematic entities do not exist, according to the pretense we engage in when using the discourse, they do exist”. According to such a fictionalist view, one might engage in conventional discourse without positing that the entities referred to in such discourse ultimately exist, for example, through adding an operator “in fiction F” (or “according to the conventional domain”) to any truth claim. Hence, on a mindful buddha account, a buddha may be said to use language “under erasure,” employing words while remaining mindful that words do not actually refer in the way they purport to—mindfully aware that referents are nothing more than fictions.

I, for one, agree and approve of this explanation.