No, it wouldn't, given that all of the premises are true and known with a very high degree of certainty.

I know you're trying to set up a clash between moral intuitions and the general rule, and in general that's a good way to try to proceed (because most of our moral judgments are initially intuitive, and we then use rationality to verify, reject, or unsoundly rationalize them). However, I'm paying attention, so I'm not going to randomly stumble into this without thinking things through.

What you've said is that this man is cognitively dead. Everything about his old self is gone. He's never coming back; he's just dead. But, if we wait nine months while pouring lots of resources into the body, we can get in-effect-identical-twin of him.

Now, in this case, you might be able to make the virtue-ethical argument that even though we rationally understand that the original person is dead, and that the body has (for now) no personhood, and a new person won't reappear for months, because it's a grown man's body, any steps taken to kill him would damage the virtue of the people taking those steps: they could not help but either grow substantially more callous towards human life, or be psychologically damaged themselves. In order to be morally virtuous in the relevant cases, we therefore have to go through the motions of moral virtue in this case, even though it isn't a moral issue in truth. Because we don't have direct access to others' mental states (or the lack of them having any mental state), it's especially hard to fully emotionally accept that this person who looks just like any other person is actually just a body with no corresponding mind. But, as I said, we're pretty good at these things. Maybe we can do that after all. Maybe there isn't even a virtue-ethics argument that works here.

But we needn't worry overly much, because realistically, your hypothetical scenario's premises do not match the kinds of situations we normally encounter. In fact, we don't know whether or when people will wake up from comas (unless they were medically induced), and generally even with severe amnesia there is still a considerable amount of the person's original mentality left. Almost all the difficulty in the real world comes from uncertainty.

It's reasonable to have a debate about what age of fetus corresponds to an acceptably low risk of any significant degree of personhood. But it's not so reasonable to just say, "Well, anyone gets to feel what they feel and say a number, and you have to treat that number with the same respect as careful research into the biological state of the fetus."