One of the great “what ifs” of WW2 involves the Prince of Wales and Repulse. The British planned on sending an aircraft carrier with them, HMS Indomitable. However, on November 3 Indomitable ran aground in the West Indies during her workups, and she had to put into Norfolk for repairs.
The big question is whether an aircraft carrier would have provided the air cover to keep the slow Japanese bombers away. We can discuss more of that next week.
Off the cuff, I would say the Illustrious would have just been sunk with the others. After all, the Illustrious at this time only had a complement of 33 aircraft with the bulk of them being Swordfish bi-planes. The fighter complement consisted of the 805dt squadron made up of about 12 Fairey Fulmar fighters (hardly a match for the Zero). The only thing that really would have protected the Illustrious from the same fate of the Repulse and the Prince of Wales would be its array of anti-aircraft guns which likely would have been insufficient.