The third ability of Aang's Iceberg allows you to sacrifice Aang's Iceberg as the ability resolves, not as a cost to activate the ability. If Aang's Iceberg leaves the battlefield before the activated ability resolves, you will be unable to sacrifice Aang's Iceberg and will not scry, even if Aang's Iceberg was sacrificed via a different ability while its activated ability was on the stack.