Is your other point that witnesses and proclaimers of the gospel MUST die for the necessary efficacy to be activated? Not too sure what you mean.
Only 1st century church or 1st hand witnesses who were appointed by God to spread the gospel. These are the people who were given the gifts to help them spread the gospel- basically, Jesus spoke through them until Jesus' words and action were recorded in the scriptures.
They were not given authority to appoint others in a never ending cascade, Jesus' words are now with us in the scripture and they are spirit.
Paul forbade some of his crew members from teaching because they were not appointed to do that:
1 Tim 1:
1Paul, an apostle of Christ Jesus by the command of God our Savior and of Christ Jesus our hope,
2To Timothy my true son in the faith:
Grace, mercy and peace from God the Father and Christ Jesus our Lord.
3As I urged you when I went into Macedonia, stay there in Ephesus so that you may command certain people not to teach false doctrines any longer
4or to devote themselves to myths and endless genealogies. Such things promote controversial speculations rather than advancing God’s work—which is by faith.
5The goal of this command is love, which comes from a pure heart and a good conscience and a sincere faith.
6Some have departed from these and have turned to meaningless talk.
7They want to be teachers of the law, but they do not know what they are talking about or what they so confidently affirm.