Posted: 05/09/2013 at 09:41
There's an excellent book called 'Rejuvenating a Garden' by Stephen Alderton'. He recommends your half at a time method.
If you do find any branches developing yellow/brown leaves and dying back next year, cut them out before it spreads. I didn't take action quickly enough.
You're not likely to kill it. We re-chopped one that had got a lot of die back, right back to base, this spring. It's already a metre high.
Digging out would be a major job and new plants take a lot longer to achieve a barrier