Do you have any leaves coming on with your crape myrtle? If it’s alive, you should have leaves growing now. If there are some healthy branches with leaves and others that are black and leafless, you could prune out the dead branches. It would be worth finding out what is wrong with the shrub that is causing black branches and trunk. Is there poor drainage causing it to rot? Or, problems with the roots? I would take a picture and check with a garden center manager or your extension agent and ask for advice.
Thanks for writing!