Hi Don, Kimberly here at landscape-solutions-for-you. Thank you for asking the question on your scorched Oleander plant. I am sorry to hear about the xylem problem as this can be terrible for a plant specimen. The root sytem is extensive and my concern with new growth is encountering the same problem. If at all possible, dig around the Oleander and find the crown roots. This is your tap or main root. If you can pull it out that would be ideal. If not, purchase some glyphosphate herbicide and pour over the crown roots. This will kill them off. If you have any new growth, you can apply the herbicide to the new growth. This is an environmentally safe product, but still use caution when using it.
The other options is to kill off the crown roots, and wait to see the new growth and the development of its health. Oleanders are beautiful plants and I hope there is a way for you to save it or remove it.
My crew and I have removed extensive shrubs and trees before and the main objective is to get the main tap root. We have used chains and my pick up to remove the base of the trees or shrubs. If you have a pick up and chains, this may be an option for you instead of hiring a landscaper. The best of luck to you and let us know how you made out.
Thanks again for asking the question here at landscape solutions for you. Have a great day!
Kimberly