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Maybe the miniature "Sacramento".

https://www.crapemyrtle.com/store/c2/Miniature_Crape_Myrtles.html

These articles will help you.

https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/pruning-crepe-myrtle-trees.htm
https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/best-crepe-myrtle-pruning-time-when-to-prune-crepe-myrtle.htm
https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/transplanting-crepe-myrtle-trees.htm

Yes, this was likely damaged when the root was cut. The old shrub will not likely recover anytime soon.

You will want to select a new cluster, or single branch to become the new shrub. Keeping this shaped will require constant pruning of the basal shoots until they stop forming. This could take a year or more.

You could also leave it to grow naturally, but it will become quite unmanageable and prone to disease if left this way.

The problem seems to be a mold issue. Luckily the problem tends to resolve itself over time. Sooty mold will commonly affect crapemyrtle. This article will help: https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/crepe-myrtle-tree-problems.htm

There are several varieties of crapemyrtle that will survive in ground in your area. In container they will likely survive as well, however, if you are concerned about those really cold nights, then You could also bring them inside if they will fit. Otherwise, put them next to a south facing wall, or mulch them well. Here is an article for more information: https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/tips-to-grow-crepe-myrtles-in-containers.htm

It is possible that the primary stem and foliar crown has died back for some reason, water deficit (drought stress) is very common. But the lower trunk and root system is still viable and putting up suckers. If you select one sucker, in the highest position on the stem, to grow up and become the primary tree trunk, it may or may not develop as the same cultivar with flowering characteristics as the parent tree. You can water, wait and see, or replace with a new tree.