Board Thread:Naruto Discussions/@comment-4682609-20140806081616/@comment-3568954-20140806092119

the thing is that if they go blind it will likely take many years and the simple reason is this

he didn't just get obito's eyes transplanted again. this time Kakashi's normal eyes awakened the sharingan meaning they are brand new sharingan they are simply Mangekyou sharingan and they have access to obito's techniques. he may have meant that his visual prowess in the eyes are temporary and that once they fade kakashi will have his own sharingan