good question.
from the srd:
Mirror of Opposition
This item resembles a normal mirror about 4 feet long and 3 feet wide. It can be affixed to a surface and activated by speaking a command word. The same command word deactivates the mirror. If a creature sees its reflection in the mirror’s surface, an exact duplicate of that creature comes into being. This opposite immediately attacks the original. The duplicate has all the possessions and powers of its original (including magic). Upon the defeat or destruction of either the duplicate or the original, the duplicate and her items disappear completely. The mirror functions up to four times per day.
Caster Level: 15th; Prerequisites: Craft Wondrous Item, clone; Market Price: 92,000 gp; Weight: 45 lb.
Mord’s Disjunction
Abjuration
Level: Magic 9, Sor/Wiz 9
Components: V
Casting Time: 1 action
Range: Close (25 ft. + 5 ft./2 levels)
Area: All magical effects and magic items within a 30-ft.-radius burst
Duration: Instantaneous
Saving Throw: Will negates (object)
Spell Resistance: No
All magical effects and magic items within the radius of the spell, except for those that the character carries or touches, are disjoined. That is, spells and spell-like effects are separated into their individual components (ending the effect as a dispel magic spell does), and permanent magic items must make successful Will saves or be turned into normal items. An item in a creature’s possession uses its own Will save bonus or its possessor’s Will save bonus, whichever is higher.
The character also has a 1% chance per caster level of destroying an antimagic field. If the antimagic field survives the disjunction, no items within it are disjoined.
Even artifacts are subject to disjunction, though there is only a 1% chance per caster level of actually affecting such powerful items. Additionally, if an artifact is destroyed, the character must succeed at a Will save (DC 25) or permanently lose all spellcasting abilities. (These abilities cannot be recovered by mortal magic, not even miracle or wish.)
Note: Destroying artifacts is a dangerous business, and it is 95% likely to attract the attention of some powerful being who has an interest in or connection with the device.
I'd say the mirror duplicate is a magical effect that can be disjoined bt whether it would go away if the mirror is destroyed is a good question, by default I think no, the duplicate lasts until it or its original is defeated, but if the duplicate is a sustained effect that must be maintained by the mirror then yes.
