I am in a watching mode over here. Same thing happened to my new one planted last year. The wood underneath is still green so I am hopeful but the next month should tell me more. Maybe someone has a better answer for you then mine since it's a wait and see.
Cher

So my question is, what is the prognosis?

===>> the prognosis is to wait another month and see what happens ...

ken

I doubt your crApe myrtle is dead, but it may have to resprout from it's roots as it did previously. Only time will tell.

I'm happy to report that our Crepe Myrtle is very much alive. New growth is appearing on about 80% of the twig structure so far and the growth looks very healthy. We we are excited about this. Thought you all would like to know.

My crApe myrtle collection here in TN did the same thing. Of course mine were established, so I wasn't really worried about them. They are almost back to normal now. Glad yours made it too!

Glad to hear yours if fine. Mine has releafed also.
Cher

Crepe myrtle shrubs are pretty tough. It will probably be fine. I had a large crepe myrtle at my old house, and I don't think I could kill it if I tried. Like many others are saying, just be patient and wait to see what next month brings.

Apparently plantingman didn't bother reading the follow-ups.

In places where crape myrtles are marginal, they have been known to die back to the ground every year! Some neighbors in the high desert had a crape myrtle that did this.