Red Mage is a combination of Mage, healer and supporter. Their abilities and options, both magical and non-magical make them a great asset to anyone who has them as an ally. The Red Mage's re-roll and double-cast abilities make them a very potent ally or enemy.
Each red mage is different so their daily lives differ from one by one. It is incredibly that some red Mages are focused and self-disciple, training and studying before other characters get up, and continuing their work well after everyone else falls asleep. There are also some red Mages that are incredible lazy, getting up well after everyone else has gotten up, spending their days screwing around, goofing off and doing nothing productive. But each red Mage is different, so no two red Mages spend their days exactly in the same manner.
There are lots of red Mages who have done things worthy of being remembered. One of the most notable red Mages is Jack the Red, who was one of the earliest known red mages and the whole reason red mages are referred to as "red mages". Jack the Red was a human red mage who, along with a party containing an elf rogue, a human fighter, & a half-elf healer, helped saved the world from the demon-knight Garland. Another notable red mage was Fradino the Scourge, an evil Aasimar red Mage who ruled the Ullastian Empire with an iron fist. Deborah was another notable red Mage, who grew so powerful and mighty that she became a goddess.
In their ranks, several organizations have red Mages except for those which are extremely Mage-phobic. And also there have been several cases where red Mages have founded their own organizations, recruiting other red Mages and dual nature characters. Some of the most notable organizations founded by, controlled, or involved with or by red Mages are The Cloak and Staff Society, The Mages of Scarlet, Nightcasters United, The Order of Radut.
It is not hard to see that each NPC has a different reaction to red mages. Most common folk don't really care about red mages unless they need healing or a red mage is destroying their homes. Mage-phobic NPC view and treat red Mages with the same hatred, fear and disgust that they have for every other spell-caster. Adventurers often bring along a red mage or two as a backup healer & a support character.
Each race reacts differently to red mages, since not all red mages are the same. Due to the dual natures, the way Red Mages treat other classes, how other classes treat Red Mages, varies, though Red Mages get along best with Bards, Duskblades and Mystic Warriors.
In the Final Fantasy XI, red Mage can fit into a campaign just fine due to their versatility and adaptability. If you are doing a Final Fantasy style campaign, this class is absolutely required. Red Mage NPC can act anyway you want towards the party, whether it is friendly, antagonistic or indifferent to them.
To adapt the red Mage, one is to make a red Mage that is a divine spell-caster instead of an arcane spell-caster. Another is to have a red Mage that focuses more on one attribute than others, such as a red Mage focus on spell-casting with access to a higher spell level but at the expense of their base attack bonus plus their weapon and armor proficiencies or a red Mage focuses more on combat with better hit dice, base attack bonus, and/or better weapon and armor proficiencies but with less spells per day and known, possibly a inability to cast some of the higher level red Mage spells.