Guild Mages are a type of character found often in a group of heroes (I think it has been years since I played in a group that didn't have at least one mage in it (not counting the few times I played in Havena, where magic use is forbidden)) so there shouldn't be much need for NPC mages to help the group and most NPC mages seem to be destined to become villains, right?
I beg to differ: the options mages (and other magic users) can choose from cover such a vast spectrum, that you can easily have a number of mages work together with each having his or her unique area of expertise.
Even two academies teaching the same general topic will differ in game stats and mindset.
This gives a lot of room for collaboration and ingame discussion about the merits of specific spells.
For this purpose I like to let hero mages encounter NPC mages occasionally to give them option to interact with a colleague outside of a direct confrontation with a villainous mage.
To go for further education in the form of a secondary study is quite common amongst mages. Their network of academies is set up to do this and it benefits the academy as well as the student. Most mages opt for their secondary study to be at an academy of their own guild as the administrative hurdles to change guild allegiance or receive an exception permission to study at an academy belonging to a different guild are quite high. Further information can be found in Magic of Aventuria, pages 72/73
For this example we will therefore look at someone who initially studied at the Kuslik school of anti magic followed by a study at the thorwalian school for clairvoyance in later years.
Both profession packages can be found in Magic of Aventuria (p184 & p188) including their magic style special abilities. These special abilities give little bonuses unique to the academy to support the spells tought there. So someone from an anti-magic academy will be a little bit better with those special abilities in anti magic spells than someone having learned the same spells after attending a different academy. In addition each magic style unlocks three advanced magic special abilities.
So our mage will want to have these two magic style special abilities:
Scholar of the Kuslik Hall of Anti-Magic (MoA 98) & Scholar of the Thorwal School of Clairvoyance (MoA 100).
To be able to use two magic style special abilities we also need the Magic Style Combination (MoA 94).
Let's now have a look at the story how an arrogant court mage trained in Kuslik and looking down onto other mages changes their ways and comes to study at the free spirited academy in Thorwal.
Being a court mage is a highly revered position, typically coming with a nice salary,
political influence and best case a lot of time and other resources to let you do obscure research.
He became sidetracked by some research into old artifacts and when stuck, lacking in clairvoyance expertise, was then given the chance to attend the yearly Hesinde Dispute in Thorwal. That this offer was arranged by the counts brother should have been a hint but curiosity for getting a clue on a research breakthrough prevailed and after a long winter the new count, brother of the mysteriously deceased former count had his own court mage he trusted more than the person who wasn't there to do anything about the terrible loss of his beloved brother. Disenfranchised by the machinations of courtly intrigue a life as adventurer awaited and when the next winter approached, Thorwal was again the destination. Over the years living as an adventurer, spending the winters in dispute and learning clairvoyance spells eventually lead to a secondary study in Thorwal. And to a much more relaxed and friendly person, still curious but not arrogant.
