Here's a quote I found for you.
It doesn't say whether or not it is permanent, though.
But reading this short explanation looks like the clubbing could possibly go away if oxygen levels in the blood rose back up to normal.
"Clubbed Fingers are a type of finger deformity that can be caused by a number of diseases. Finger clubbing involves a excess growth of skin underneath the fingernails. As a result, the fingernail curves downward and it takes on a round appearance. Clubbed fingers are usually a symptom of a heart or lung disease where oxygen levels of the blood drop below normal." http://www.mahalo.com/clubbed-fingers