In that situation medical professionals are doing everything they can to keep that person alive. If there is another option besides the one donor found it will be used.
Fetuses aren’t granted the right to “pursue happiness”. Abortion doesn’t absolve a mother of obligations while giving the child a chance to part ways amicably. As the potential organ donor you cannot choose to actively terminate the life of the recipient, they are free to continue on until they can no longer.
Those have no bearing on the autonomy of the donor. The ethicalness of declining to donate isn't contingent on support of medical professionals nor the concept of active or passive action.
What does supervene on the ethicalness of the action is autonomy. Bodily autonomy gives a donor the right to back away at the last minute, not the concept of passive action or medical support. I'm not disagreeing that those exist, but they don't lay the foundation for the ethicalness of the action - bodily autonomy does. No one, not even the government, has more say over one's body than oneself.
Parents have an obligation to the care and development of their children. There are plenty of parents who are found guilty of negligence. That is more appropriate than the donor concept.
Parents are not legally obligated to donate their organs to their children even if it would result in saving their child's life. The reasoning behind this is that people, including parents, have bodily autonomy.
The donor concept is a perfectly valid parallel. I can understand that someone wouldn't like it if it challenges their conclusions, but that's sort of the point. No one, not even the government, has more autonomy over ones body than oneself.
Fetuses aren’t granted the right to “pursue happiness”. Abortion doesn’t absolve a mother of obligations while giving the child a chance to part ways amicably. As the potential organ donor you cannot choose to actively terminate the life of the recipient, they are free to continue on until they can no longer.