A copy of Tuvok's katra was inside Lon Suder.
Janeway could have just as easily ordered that Katra to overwhelm the Betazoid's personality, or the Doctor could have chemically suppressed Lon's Distinct higher functions.
But the argument that swayed the captain was that Kes loved Neelix.
Tuvok didn't have an advocate, although apparently Janeway knew his wife.
Probably had dinner with her lots.
"If it looks like he's going to die and my husband can't get home to me in time, I highly recommend that you offer yourself as my surrogate. He's actually quite talented"
Until Kes started crying
, Janeway was of a mind to let Tuvix live.
And we all know that Kes' love for Neelix is infinite and forever.
Thank god they're so stable and intertwined.
Although if Tuvix wouldn't have kept trying to get his leg over, then Kes wouldn't have had such an extreme reaction to never again bumping fuzzies with the kitchenrat.