With injector failures, you start to get occasional rough idle which progressively gets worse. You can get fault codes being flagged and you may find the injector resistance isn’t to spec... Cost to fix should be free as Holden should replace them all under factory warrant or good will (statutory warranty), presumably with injectors that don’t have thie defect (but Daniel Sousa seems to be having the same issue with the replaced injectors)
As for lifters, supposedly these need periodic precautionary replacement at 100,000kms though it’s not documented on any official GM/H doc I’ve seen. Rockers on the other hand are a known issue as the roller cage can wear and the rollers fall out which isn’t great. This is a different issue to the defective rockers installed in some LS3s and all fixed via (ghost?) recall... If you have issues with lifters or rockers, you’d start to hear squeaks and ticking sounds that may progressively get worse... and then bang, something may break or you get shiny flecks of metal in your oil... both not good...
