Could well-maintained Malta-class carriers have remained in service into the 1980s or 1990s like the Midway class?
Short answerYes; their size and late-1940s completion date could plausibly have supported 30 to 40 years of jet-age service.
NotesHMS Hermes and the Audacious class provide the comparisons for a Malta air group of Phantoms, Buccaneers, Sea Kings, and fixed-wing airborne early warning aircraft. This is explicitly counterfactual, but the service lives of built carriers make continued operation into the 1980s or 1990s plausible.