Q.oleanders
Half of my 20 year old oleander hedges have died. They look horrible. What do I do? I’ve heard that it’s next to impossible to uproot oleanders.

Cutting them back to the ground is one possibility. If by chance some are still alive, they should grow back next year.
Here are some other options. Removing dead shrubs should be easier than live ones. Even if you can't get all the roots, completely dead ones won't grow back.
https://www.gardeningknowhow.com/ornamental/shrubs/oleander/removing-oleander-bushes.htm