Doubt starfleet would really charge her with anything. I mean it would be very bad press. Also starfleet may agree with her because of the circumstances since it was thru the transporter. Also. Tuvok was a valuable officer and post dominion starfleet needs all the valuable people it can get. That doesn’t make it right but again I doubt she would ever get in trouble.There's nothing wrong in saving the life of anyone as long as it's not at the expense of someone else. If your resuscitation depends on sacrificing someone else, someone who's unwilling to be sacrificed at that, I mean even if the person was willing I still think it would be wrong, like it is wrong to buy organs from living people who are so poor and desperate that they are willing to accept mutilation for a little money. If it's is wrong to do the latter and I believe it is, it is even more wrong to do that to an unwilling being. What Janeway did is just murder. It's cold-blooded premeditated murder! If there was any justice in Starfleet and there can't be because it is just a show and justice is just a fleeting incoherent thing in that context submitted to the vagaries of undeterminate writers. So if there was any justice in that fictional world she would incur the punishment for murder in the first degree with aggravated circumstances because she thought about it and did it in full knowledge and responsibility and using her power as a leader.
Starfleet would probably rule it justified homicide.
Also if tuvix was willing to under go the process (which should have been done in the episode)
Then there should be no problem with it. Just like with sim or anybody else who willing sacrifice themselves for their crew mates. I mean it is his life if he wants sacrifice himself or not, the choice is his.
Also buying organs is illegal and you can only volunteer to give them up, so you can’t sell them.