The wizards of the Black Company series are very different from the ones in Dresden.
Spoilers for The Black Company:
Even a minor wizard like Tom-Tom was able to resist death far longer than a normal person would. It didn't help him (since Croaker didn't know how to repair the damage) but he lingered. As for Limper, he sometimes left parts of himself behind and he never fully recovered from those injuries. Hanged Man had that broken neck and another one (I want to say Bone Cruncher) had that scar from a blow that almost killed him. Most of the male Taken also looked as if they had spent centuries buried alive because they didn't see the need to use magic to fix their looks.
And when the Taken fought Taken (or powerful members of the Circle) they died - which is why so many of them faked their deaths (not wanting to meet an equal and maybe die).
Maybe the best way of handling people like that is kind of a reverse Death Curse. Say that when they are near death they instinctively use their powers to heal themselves, or at least preserve themselves. Not so that they can keep fighting but so they can survive. Yes, that is a bit self centred, but none of the Taken struck me as beings that would die for a cause.
It would need to be cast unconsciously, maybe...
Sponsored Magic: The WILL to Survive
When faced with death you can cast Thaumaturgy, incurring debts, to keep yourself alive. Not alive and functioning and maybe not even alive and well. Indeed, you'll be in such bad shape that odds are others will think you're dead (i.e. Taken Out with fatal consequences). It will take you a long time to recover fully - every debt taken to survive adds X time to your recovery - but you will be back because you Refuse To Accept Death.
And you could flesh out this power - say that using it allows the person to take extra consequences that will take longer than normal to buy off. Say upping the recovery time to the level above what it normal takes (mild recovers as moderate, etc) or something like.
Call it a -1 refresh power because it's useful but only in a very limited set of circumstances (i.e. when you're being defeated) and say that you can only take it if you have both Evocation and Thaumaturgy. Heck, you might want to restrict it to those who have at least the starting Wizard 'musts' because lesser talents lack the ability to dig this deep when needed.
Green Ronin did a D20 type game based on the Black Company setting and you might want to mine that for inspiration on Taken level wizards.
Richard