[honestly, that 'genius' comment grates on Kaz, but he's not about to snap at the only other guy who seems to have a head on his shoulders.]

Nanomachine tech or symbiotic parasites that rebuild people on a cellular level aren't implausible, either before or after they die. Does anyone actually remember the experience of death?

What do you mean by 'base brain'? Unless I'm missing something, successfully fooling all sensory input would chain straight up to all higher levels of processing. And I'm still going with that as a more plausible answer than 'hostile alien'.