How an available Formidable might have changed Force Z

If HMS Formidable had not been needed to replace Illustrious, could she have changed the fate of Force Z?

Possibly. A carrier reserve near the Indian Ocean could have supplied fighters, fighter direction, and stronger escort coordination against the unescorted Japanese bombers.

This is a counterfactual rather than a prediction. If Illustrious had remained available, Formidable might have been stationed near the Indian Ocean with the option to reinforce either theatre. A carrier attached to Force Z could bring Fulmars or Sea Hurricanes against Japanese bombers that arrived without fighter escort. Even modest interception could disrupt attack runs, while carrier command facilities could improve fighter direction and coordination with land-based aircraft. Additional cruisers accompanying a carrier would also deepen the formation's anti-aircraft fire.