I know she's smarter, better, and stronger than I and would find a way to help explain and educate this woman on how she's pissing into the wind wrong....
But I can't help but imagine Janeway just kicking the shit out of that foxbot on principle and for the security of the federations reputation.
If Tuvix retained Tuvoks skills, keeping Tuvix would mean not having to deal with Neelix, however. Im sure she considered that as a reason to keep Tuvix, before her bloodlust won out.
Nah, there was the clear risk that Tuvix exhibited the worst traits of Tuvok and Neelix. That would be a total nightmare. Restoring the original was the proper choice. At some point an opportunity to get rid of Neelix could appear, and you could retain the original Tuvok without loss.