I think the answer to your question is contained in this part of how you worded your question. Judas' status as the apostle who would betray Jesus is an extraordinary one that the other apostles, of course, did not also share in. This is confirmed by the fact that Judas' betrayal is framed as a specific fulfillment of specific OT prophecies (see Jesus' quotation of Ps. 41:9 in John 13:18; cf. John 17:12; Peter's appeal to Ps. 69:25 and Ps. 109:8 in Acts 1:16, 20). A component of those OT prophecies is that the prophesied betrayer would abdicate his inheritance and office by his betrayal ("May his camp become desolate, and let there be no one to dwell it") and would have his office filled by another ("Let another take his office"). Judas is replaced not just because he died, but because the Scriptures had previously spoken to that end and had to be fulfilled.
Thanks. So the ultimate reason for his replacement was not that there had to be 12 apostles (since at one point there were 13 or maybe more), but as a further judgment upon Judas?
I think so (?). Consider that Peter’s argument for why someone must be appointed to replace Judas in being “a witness to the resurrection” is based not in the fact that there had to be 12 apostles, but in the fact that the Scriptures had to be fulfilled to that end (Acts 1:16-25). A question that could be raised is the numerical significance of Jesus having appointed twelve apostles to begin with and if that is relevant here, especially considering that John describes the structure of the walls of the new Jerusalem in terms of 12 gates (12 tribes of Israel) and 12 foundations (“on them were the twelve names of the twelve apostles of the lamb,” Rev. 21:12-14).
Maybe split similar to Joseph's tribe?
Paul is not one of the 12. Paul was a special apostle. He's not called to replace anyone, or fill up the number 12.
