תרומת איברים ובוא המשיח

I've asked many rabbis about this, none have been able to give me a good answer. I've heard about how when the messiah comes, it is very important to have all your organs with you, for reincarnation. But then, there is the issue of organ doning. If you, G-d forbid, die in a car accident, and they are able to save your heart, doesn't it seem selfish to want to keep it, just for reincarnation, when you can save another's life? Doesn't this contradict the most important mitzvah, to save another's life? Secondly, when the messiah comes, all these amazing miracles are supposed to happen. The dead will be reincarnated, etc. With all these miraculous occurances, wouldn't it make sense that G-d would give you a replacement organ, since you donated yours to save another's life? With all the miracles supposed to happen, this wouldn't seem so far fetched to me.Well, that's been bugging me for quite some time. I hope you can help me. Thank you so much for your time!!