Probably will grow back, not sure I'd take it to the ground, probably leave a few inches above ground - but wherever you cut it to, don't do it before mid March, April if you're in the North.

Are there any leaves fairly low down? You can cut immediately above a leaf joint and it will grow back strongly. If you are giving a very hard prune to an existing old shrub, I might suggest staggering the job over two years - cut half the stems one year and the other half the next. Also, give a good general feed after the pruning

The ones at Bodnant were pruned with a chain saw a few years back to about a foot high. they have grown back beautifully. As said give them a good feed after pruning.