Yep, it was a particularly striking problem this year.

Hard frost killed the leaves before they naturally fell (abscissed). Same with Japanese maples.

Will they drop for new growth in spring?

As long as the plant is still healthy, yes.

Mike, be patient with them in the spring. Here most years my Crapes are more like perennials, the branches die back to 6 to 8 inches up from the ground. Last winter was warm, just some tips died on my established ones. This year I expect them to give me twigs for the bonfire in late May as soon as its obvious where our cold winter has killed them down to.

The dead leaves remaining on the trees have nothing to do with the living status of the tree; they are there because many of us in the East did not see s normal progression from Summer to Autumn. (As Dave says, I see the same thing on my Japanese Maple and my forsythia). From August through October it was abnotmally hot, and then it very suddenly changed and we had deep frost. In fact, I expect less damage than last winter, assuming the rest of the winter is somewhat normal. Last winter was so warm in February that my favorite Crape Myrtle tree’s trunk split in half as a result of alternating winter heat and cold. Even that one, eventually recuperated fully from the roots in the same season.