When people fail and fall, as Judas has done, requiring the choosing of a new member of the 12 here, we can be left in quite a quandary. Obviously, in the case of Judas, his fall had been heavy and significant. At the same time, as Peter explains here, Judas’s betrayal actually fulfils part of what has been prophesied in regard to the death and resurrection of the Messiah.
This is one point where we can find ourselves in difficulties of understanding around failing and falling in our Christian lives. I’m not a huge fan of the doctrine of predestination (either single or double predestination) but it is undeniable that whereas our perspective is only ours, God has a view of our lives and circumstances which is far wider, far more knowledgeable, and far more in control of things than ours ever will be. That isn’t to say that failing and falling is something we should try to do because it doesn’t matter, far from it. But when we do, it is not beyond the reach or love of God to bring about redemption and reconciliation.
Second, and following from this, the Church is bigger than any one of us. It is not about any of us individually. It is about a community of people, holy nation, called to live lives surrendered to God, with a direction of travel towards Him, and lived in such a way as to draw others in to relationship with Him. One day soon, though, none of us will still be here. All the worry, anxiety, energy, power-brokering and so on that we will have done to try and push our own claims or theological points of view will cease, as we entrust the care and growth of the Church to the next generation. It is not for us to conserve our view of Church as we see it, or as we wish it was. It is for us to rejoice as God reveals ever more of Himself to His children with each passing generation.