And then he was never heard from again.

I love God's sense of humor.  Check this out.

Acts 1:21-26(NKJV)

“Therefore, of these men who have accompanied us all the time that the Lord Jesus went in and out among us, 

beginning from the baptism of John to that day when He was taken up from us, one of these must become a witness with us of His resurrection.”

And they proposed two: Joseph called Barsabas, who was surnamed Justus, and Matthias. 

And they prayed and said, “You, O Lord, who know the hearts of all, show which of these two You have chosen 

to take part in this ministry and apostleship from which Judas by transgression fell, that he might go to his own place.” 

And they cast their lots, and the lot fell on Matthias. And he was numbered with the eleven apostles.

So Matthias was the official replacement disciple….and he was never mentioned in Scripture again. 

Why was it so important to describe how the replacement was chosen and who it was if that person was never mentioned again?  I sometimes think God puts stuff like this in there to tease us and see if we are paying attention!  :)