Yeah that stick is likely as good as dead, but lilBush06 is right it could recover.

Next time that happens try half watering the cube and spraying with a water mist. The plant will take in moisture faster though the leaves and stems. Also not saturating the cube will make it easier for the roots to recover. I have saved many a mother plant by spraying the deadlooking leaves only to find half of them come back.

Spraying is also a great way to feed the plant if you are fixing a PH problem. If your plants are starving from fert buildup or minerals or somthin, just folliar feed. Speeds up recovery time quite a bit. Also Rockwool can be tempermental. Try using a half strength solution for a week or so then flower that girl!