Wamberal,
Horan retired and guys called Grey and Giteau came along. We still made a RWC final with Elton Flatley at 12. Hell even To'omua is looking very good there and likely will only improve.
Since Eales moved on players like Sharpe and Vickerman came along.
Yes we haven't had as good a number 8 since Kefu, but also when David Wilson retired George Smith came along. Swings and roundabouts.
Your post is extremely arrogant and ignorant, assuming that every player from the past is better than the current. Many of the current replacements have qualities that their predecessor's lacked (E.g. Vickerman was much more brutal in cleaning out than Eales ever was).
As I said, Hunt was a better NRL fullback than Izzy. It's not unreasonable to think that he could in fact make a better traditional rugby fullback than Izzy. Might not too. Just saying one player, no matter who, isn't the end of the world and worth changing the way you do things over.
Also Dave Beat, not sure I'd bring up Rocky Elsom OR Dan Carter as a reason for sabbaticals. Rocky left and never came back the same. Carter went to Perpignan , got injured and missed a bucketload of rugby, and some could argue hasn't been quite the same since.
The important thing to remember too, is that New Zealand has more depth to cover this stars in the case of injury or burn out. A McCaw sabbatical to stay fresh and peak at the right time is one thing. A Carter sabbatical to make cash, get injured and miss about 10 months is a completely different thing.