No conifer will regrow if cut back to brown material, if they are too big you will need to remove.

I have tackled this on occaisions in the past, and they do come back albeit very slowly, its up to you but if it were me, i would start again that means cutting back to the main trunk, with all branches/ foliage removed, it will look very sparse but over the course of the year you will notice new growth breaking out all over the bare trunk,by trimming in all over the bush i have found this way to be less succesfull, an eg here for you, three years back, took a yew tree down by half, inc all lower growth, what was left was a fifteen foot trunk, now its all foliged up and tightly clipped, but you have to be patient and thats all part of gardening, are they close to the house? hope this helps, i can post pictures of the tree mentioned and will try to post these in the next week or so. hope this helps, julien.

Moongrowe is correct on cutting back to old growth on conifer and they will not respond, but we are talking about Yew here, which will respond to renovation pruning, julien.

Your right Julien I wasn't thinking, you can actually cut a yew down to the ground and it will regrow.

There used to be a huge old yew growing by what is supposed to be Little John's grave in Hathersage, Derbyshire. The large yew was gone but there was a beautifully kept clipped yew about 10 or 12 feet high, which I assume had regrown from drastic pruning. But I can't tell you how far the tree was cut back or how long it took to regrow. I have a baby yew grown from seed and it is still very small after five years, so I would go for cutting back rather than replanting. And this would avoid the difficulty of removing the roots too.

If you cut it back and for some reason you don't like the result you can always decide to remove them later if you want to.