Pando is amazing, and my younger self would have wanted a piece of it to memorialize as a bonsai. But my more mature self would not do it.
First, trees in private collections rarely live very long. Be honest, how many plants have you had in your collection that have died? How many plants have persisted for more than a decade? How many more than 2 decades in your care? Plants, trees, bonsai in private collections die pretty regularly. Public collections are only incrementally better at keeping rare specimens growing. Collecting trees is not like collecting coins or baseball cards. We are all human, when I accidentally killed a pomegranate tree that I had successfully kept growing for 41 or 42 years, I was devastated. Not only had I lost an "old friend" it was time into a project I could not live long enough to replicate.
It also caused me to rethink this idea of keeping rare specimens. You know bonsai is about appearance. In general, at bonsai shows, the judges do the judging "blind" in that they do not read anything beyond the species name of the tree if they don't recognize it from the foliage. The appearance of the bonsai when shown is all that counts. Not how the tree "could look", and none of the history of the tree counts in the judging. Judging is about the image presented, nothing more. Hand outs, photos, long typewritten descriptions of provenance do not add anything to the points when judged, appearance only is what counts. At some shows, there is a category for educational exhibits, where a 'Pando' clone would clean up on ribbons, but as classical bonsai, the origin of the tree does not matter, it is appearance only that counts.
Yes, having a piece of 'Pando' would be an educational curiosity, but beyond that, the genetics really don't add to the ''bonsai image".
'Pando' is the only the oldest documented woody tree clone. There may be others out there, possibly older. Some of the creosote bushes in the Great Basin desert may be as old or even older than 'Pando'. They form circles in the desert, much like 'Pando'.
'Pando' is in trouble for several reasons. Deer are grazing new growth as fast as it is formed. Cages have been installed in areas to give new shoots a chance. Wolves and other predators of deer and elk need to recover in order to bring down that predation. It is also doomed in the long term for metabolic reasons. It's telomeres and other cellular mechanisms have shortened and aged to the point where 'Pando' no longer produces fertile seed or pollen. Meiosis is no longer successful. It functionally is "post-reproductive" it no longer contributes to the gene pool for aspen. It probably quit producing viable seed near 1000 years ago. Some centuries in the future it will be eventually die because its cellular machinery will no longer be able to successfully do mitosis, basic cell division required for growth and life. It may be centuries, maybe another millennium, but the future for 'Pando' is a long slow decline. Climate change is real, and likely will have its own adverse effect on 'Pando' in the near future, but I don't know what that will be.
So if you did get a piece of 'Pando' you might find it difficult to grow due to aging of its cellular molecular machinery (biochemistry). It would likely be difficult to get cuttings to root or transplants to recover from root disturbance. But you don't know if you don't try.
The above comments about bonsai judging being based on "appearance only at the time shown" is one of the reasons that there are no "bonus points" for doing bonsai with rare and exotic trees. Nobody cares if it is an endangered species or not, the focus is the appearance, the creation of an image.
Personally I was disappointed when I realized bonsai with rare species is not regarded as "special", because I like the idea of collecting rare plants. But it is a fact. And so no "bonus points" for "rare stuff". All the points are on how well the image is executed.
