Tuvok had a neurological disease that was going to drive him insane unless they got home by the 7 year mark, Tuvix would have been fine.
Neelix's single Ocmpan lung was going to ware out at around the seven year mark, Tuvix should have been fine.
Tuvok had a serial murder programmed into him that was going to stalk and murder the Maquis crew... Tuvix might have been fine?
In the Admiral Janeway Timeline... Why not recombine Tuvok with someone else to stop his rampant insanity? If Neelix wasn't up for it, maybe someother bugger would volunteer... Maybe even Janeway herself.