I would not think it will kill the azalea. I suspect that the woody bottom half lacks foliage due to lack of sunlight but I cannot tell what else is hiding in those branches (fungal issues, etc). Dead wood like that is a common problem that I used to have in Atlanta with some big azaleas. Where are you located by the way? While in Atlanta, I once tried doing some special pruning to let some sun inside but eh, it did not improve things much. And they took a long time to show new growth, about a month I think. I did some selective pruning and not a crew cut. Maybe that would have helped more.

Hints:

I would recommend pruning as soon as they are done blooming (it usually takes about 2 weeks or so to finish blooming). Do not wait until June or so to prune as some azaleas may have already begun developing new flower buds but, exactly when actually depends on one’s geographical location.

I usually do rejuvenation pruning in thirds. On year 1, I prune a third of the bush or the third longest branches or the top third. On year 2, I prune the next third. And then on year 3, I do the rest. Prune to remove crossing branches, and admit light and air.

With azaleas (and also with small leafed rhodies), you may prune anywhere along the stem. These plants have invisible dormant growth buds nearly everywhere. They will usually go into action as soon as you prune near them. Note: with large leafed rhodies, you have to cut above a growth joint.

Sometimes a healthy plant can be suddenly cut to 6" above the ground and it will come back, but you have some risk so, if you were to do this, do it only if the azaleas get a lot of sun. And yes, dormant buds beneath the bark, will sprout to form new growth after severe pruning too but not much if the plant is located in heavy shade. One can open/thin the canopy and then remove some of the top such that the bottom gets more light which induces new growth. When the new growth has gotten large enough then you can remove the rest of the growth at the top. If you see signs of fungal problems in the areas you are pruning, consider applying a fungicide then. I would also apply HollyTone (after pruning) to encourage growth.

Pinching can be used to enhance plant form. Pinch out emerging new soft new shoots.

Dead, diseased or damaged branches can be pruned at any time.

To prevent losing Spring 2021 flower buds, do not prune in the Fall. Not pruning then will also prevent the plant from getting into “grow mode” just as an early frost suddenly appears from nowhere.

Dead wood and plant debris with fungal issues should be thrown in the trash.