You can cut it back that severely without killing it, but it's a temporary measure...your azalea will soon return to it's pre-pruned height.

Azaleas have dormant buds all along their stems and will sprout from just below any cut you make.

Keep in mind too that it has already set buds for next years blooms and pruning now will eliminate next Springs flowers - the right time to prune is during or immediately after flowering.