With evergreens they way they grow is that most species do not bud or get new growth off old wood. (Yews are an exception and this makes them very durable for hedging)
For your tree, where the branches are dead it is unlikely that any new growth will "fill in" the gaps. Existing growth on that side will continue growing and as the tree grows the gaps will become less prominent.
I cannot tell the cause of the dieback. It could be winter damage from heavy salt or if there is evidence of damage to the trunk then that could be the problem.
If this is a specimen plant that you see every day you could consider removing it. If you have some patience and it's not in a critical area then just topdress and water during dry spells and you won't notice the damage in a few years.