When Mage's Impact procs, the player is invited to cast Fire Blast. If Fire Blast misses, the spell goes on cooldown and the buff is still there. Because the buff is there, the effect is displayed, even though the mage cannot cast Fire Bast, which is on cooldown.
Impact should be hidden if Fire Blast misses, to avoid confusion.
When Mage's Impact procs, the player is invited to cast Fire Blast. If Fire Blast misses, the spell goes on cooldown and the buff is still there. Because the buff is there, the effect is displayed, even though the mage cannot cast Fire Bast, which is on cooldown.
Impact should be hidden if Fire Blast misses, to avoid confusion.