“Simon, Simon, behold, Satan demanded to have you, that he might sift you like wheat, but I have prayed for you that your faith may not fail. And when you have turned again, strengthen your brothers.”
Was the Lord’s prayer for Simon answered in the affirmative? I believe it was. From the events described by Luke later in the chapter you might not think so, but there is a difference between a failure of faith and a failure of courage, no? And certainly Jesus appears fully confident of Peter’s speedy restoration, not only with respect to his fellowship with the risen Lord, but with respect to his ongoing responsibility to shepherd others.
It is not “if you turn again”, but when. The Lord himself had seen to it.