First check for signs of sooty mould aprox three/four inches inside the growth, and also signs of the conifer aphid, check various parts of the tree, the sooty mould is caoused by the secreted honeydew from the aphids that forms black mould, this is a big problem that effects conifers, the dead growth will not come back, so you could carefully take a few lower branches out leaving the trunk showing, looks good if done properly, but if you choose to do this then care is required,look at each branch and where the end growth finishes as this could be higher up the tree and once cut you could end up with gaps further up in the tree, julien.