We need 2 really - 1 to replace ROB, and 1 to replace Strachan.You don't need a developing ruck. You only need a ruck.
The issue comes if we can't get a ready to go ruck to replace ROB.
Both are out of contract at the end of the year. Strachan's contract shouldn't be renewed. ROB should be offered a contract, but may choose to exercise his FA rights - particularly if the rumours about him wanting to study in Melbourne are true.