Here is a suggestion. A tansporter is first used to make a Thomas Riker clone of Tuvix, with the original separated into Tuvok and Neelix.
Three for the price of two.
No one dies
All that does is create a new copy of Tuvix -- Tuvix 2.0 -- while still killing the original Tuvix in the course of creating new copies of Neelix and Tuvok (the originals of whom still remain dead).
Well unless the Tuvix copy is the one that is the one that is split and not the original.