tibetan buddhism, modern science and borges

So I'm reading the Tibetan Book of Living and Dying, and it keeps talking about impermanence, how everything is always in flux, nothing is constant, there is no essential. So far, I am in agreement with this, even down to our cells that are constantly dying and being born. My issue is that they also believe in the reincarnation of the soul. But this would mean that we have an essential soul that remains throughout our various incarnations, which would seem to contradict the idea that nothing is lasting. Unless he is talking merely about material things not lasting, but what is immaterial other than the soul? Why would the soul be the only exception? It seems like a way out of dealing with the fact that nothing is lasting, truly. It is sort of a cop out to say that nothing is lasting, besides our essential selves, because we do no actually care of anything other than ourselves is lasting. We just want to be permanent.
So I have thought of a way of reconciling with this idea of change and lasting forever, and as a way to connect Tibetan Buddhism with the idea of modern science that we die and that is it. It has to do with biology and the cycle of life. When we die, our bodies decay, and become part of the dirt. The worms eat the dirt, and while most of it is shat out and becomes the dirt once again, some of it stays with the worm once it gets eaten by a bird, and so on through the process of eating it ascends in the life cycle, and a piece of you is once again part of life. Maybe this is a materialistic way of viewing the concept though, a way to make it tangible to me, a Western thinker. So the higher up you get in the food chain, the more of the smaller animals you have, and the wider variety of different past animals. Through this we remain part of this material world, spread out through many animals, all at different stages.
This connects to Borges' idea that All is One, in that we are all made up of each other and remain within each other and are all made up of the same essential substances and are simply different manifestations of what is the same thing. This is also evident to me in ideas- that whenever I digest a new concept, I find that I am able to apply it to everything I have learned before, implying that everything is somehow part of one single idea.
Such as the concept of infinity that I was unable to grasp. I cannot imagine how there is a single number that is never ending, I figured it was only a matter of perspective, that we were too close to be able to see the end of it. Then when I learned about impermanence, I began to think that the only way for a number to be infinite is if it is constantly changing, unstable so that it cannot be determined, rather than a single constant tangible number.