My reference to Maida as being decisive was as a battle that the British won in a decisive manner. Has no reference to the overall campaign.
What happened in Calabria afterwards was complex. I think two books are essential basics to understand: Counterpoint to Trafalgar: The Anglo-Russian Invasion of Naples, 1805-1806, and The Most Monstrous of Wars by Milton Finley.
Counterpoint' I think makes clear that the reason there was no followup to Maida was that the Army commander wanted nothing to do with the guerrillas that Sidney Smith was recruiting and putting into action. Also, the naval strategic situation only demanded the retention of Sicily to deny the Mediterranean from the French.
Most Monstrous' is true to it's title, in describing the grim details of the Calabrian war. The sources for this book are mostly from relatively recent Italian historical research and gives what appears to be a detailed and accurate description of all of the events there. The author maintains that there was a strategic success in the Calabrian war in that it took years to finally bring it under control and in the process demanded the presence of 10,000 French troops for years. He also holds this war as learning tool for the British who by 1808 Spain had lost their moral issues about working with local guerrillas.
Of course, it is still necessary to read the books about Sidney Smith to get more of the story. What impressed me was that Smith rangled the Queen to appoint him Viceroy of Calabria with full powers over all armed forces. Smith advocated this "total command" position as being the most favorable for victory with his pointing out that this was a foundation of his historic success at Acre, he also pointed out that this was one of the "secrets" to N.'s success.