that is going to be a tough one. I assume each and every root is adhered to the tree bark. Is there a chance that the person taking down the tree can cut a slab out of the side of the tree with the orchid attached prior to felling the tree? That would be the best option. The next best option is to remove the orchid. This would be difficult without damaging all the roots. I would think that the best time to try it is at the time of new growth starting but prior to the new growth developing new roots. This would be most damaging to the orchid but there would be a chance of survival.