I want it to be feasible to chop off my wizards heads when they piss me off. THat will not be practical in a typical fantasy universe setting.
Potential weaknesses of Dwarf Fortress mages in the
far future:
Artifacts. (This cat-leather-with-microcline-spikes helmet I'm wearing doesn't just look stylish... it also nullifies magic!)
Magic being somewhat unreliable. (Maybe if you hadn't decided to have an extra drink of Sunshine, that fireball wouldn't have blown up in your face!)
Similarly unreliable enchanted servants. (Y'know... instead of fighting that wizard, I think I'll erase the mark he's using to control those !!clowns!! and then just... run for my life.)
Dwarvern ingenuity. (No adventurer has ever returned alive from the subterranean lair of the Dread Wizard Nedor... which is why we're just gonna flood the place with magma and be done with it.)
Running out of magical power, in whatever form it takes. (Congratulations, you are a scrawny old man with a fairly heavy stick. There is an army at your door. Now what?)
Godly wrath. (I tire of thee, mortal. For your petulant insults to my glory, I shall rend the very mountains from underneath your feet, and seal your soul into the heart of a mountain!)
Trickery of various sorts. (Did it not occur to you as odd that the princess was so willing to accept your marriage proposal? You should have known she studies poisons as a hobby... rather strange girl, really.)