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To help determine if the plant is dead you can prune back from the tips until you see viable greenwood. If the stem snaps easily that is also a sign of dead tissue. Although you should be seeing new growth by now, you plant may just be delayed. Be careful not to overwater the plant if you find the stems are still green and viable as plants without foliage have lower water requirements that ones leafed out. Good Luck.

From your description is sounds like spindle galls, which are caused by an infestation of pests; it could be any number of pests.
Do further inspection of the tree and look for any other signs of pest or disease.
These links will help you pinpoint the issue.
https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/crepe-myrtle-tree-problems.htm
https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/crepe-myrtle-bark-scale.htm
https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/yellowing-crepe-myrtle-leaves.htm
https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/crepe-myrtle-tip-blight.htm

https://www.extension.umn.edu/garden/insects/find/insect-and-mite-galls/
https://www.clemson.edu/extension/hgic/pests/pdf/hgic2002.pdf

Meant to say we have at least 50 crepe myrtle trees..All planted by my father in law when they lived here...thank you

Depending on the size of the branch you can use a really heavy fishing line to tie up and support the branches.
Over time it will build up strength and you wont need the support. Just remember that you tied it up and adjust it as needed.
https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/pruning-crepe-myrtle-trees.htm

You may need to supplement your Crepe Myrtle during extreme heat and dry conditions.
Crepe Myrtle do prefer a evenly moist soil, but they can be drought tolerant to a point.
Give you Crepe deep watering to a depth of 6 inches or so once or twice a month.

If this is a new planting you will need to provide much more water and should try for consistent moist soil.

Adding 3 to 4 inches of hardwood mulch will help with moisture retention and cooling the roots.
Keep the mulch from touching the trunk of the tree.

https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/crepe-myrtle-care.htm
https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/crepe-myrtle-tree-problems.htm

Root cuttings can be dug up in early spring.

https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/how-to-propagate-crepe-myrtle-trees.htm