Taxus will take a long time if it will ever recover from pruning back to dead wood. The most I would prune back is to last years growth. If pruned back to a stump it could push up new growth but that is kind of gamble as to if it will be good quality or not. The best thing to do if the bush has gotten out of hand would be to replace with smaller ones and keep them trimmed.

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Mike Maier
aka
The Plant Doc