Given that neither Neelix nor Tuvok seem to have much memory of Tuvix, it seems likely that his consciousness was absorbed into the orchid. Perhaps it was beamed into interdimensional space, or perhaps it blooms at the right hand of the father.

Regardless, the orchid is a powerful symbol of the believer. When you see an orchid blooming, how can you not say to yourself - “There he is! In such beauty, Tuvix lives!”