Someone who's brain dead will never recover.
A more apt comparison would be someone in a coma.
The life of that particular individual starts at conception.
The egg and sperm before conception are just cells of a larger person. If they are destroyed, the individuals live on
I would argue it's an actual human
Everyone has a 100% chance of dying. That doesn't gives us the right to kill them.
You do realize that a person is an individual? A fertilized egg may become no one, or it may become and individual or twins, triplets, etc.
So while a fertilized egg maybe human and you may argue it is "a human", humans are individuals and have brains, hearts and other organs. Fertilized eggs do not.
Although if we follow your thought experiment of calling a fertilized egg a human and assigning all rights at the time of conception some interesting things occur.
First of which would be Eskimospys thought experiment. You'd be morally obligated to save the embryos and not the baby.
Second, mentioned in this research, 2/3 of embryos fail to reach maturity.
http://med.stanford.edu/news/all-ne...n-of-embryo-survival-enabled-by-research.html. (This research was published in Nature a well known peer reviewed journal. I know how important that is to you.

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By arbitrarily dictating that a fertilized egg is a person you will turn the act of procreation into the mass murder of innocent "babies" on a scale that will dwarf abortion by orders of magnitude. On average every live birth will occur after one or more failed embryos die.
You can argue that everyone dies, but there is no legal or moral precedent to allow someone to have children only to allow 2/3 of them to die. Not when the other option is to simply not have sexual relations for procreation.
So congratulations continuation of the human race is either immoral or built on a pile of dead "babies".
This is why no one actually believes a fertilized egg is a person, even if they say they do.