But the departure passages I've referred to elsewhere have some relevance here. When Paul and Peter are anticipating their death in 2 Timothy and 2 Peter, for example, they presumably don't know whether every other apostle will also be dead soon. So, how Paul and Peter prepare their audiences for their (Paul and Peter's) death isn't equivalent to preparing them for the post-apostolic age. But it does have some relevance. For one thing, Peter was a Pope under a Roman Catholic scenario, so any apostle who was still alive after Peter's death would have a lesser authority than Peter and his successors. And even though Paul and Peter knew that one or more of the other apostles could outlive them, their own deaths would have underscored the potential for the other apostles to die and the need for preparing for that scenario. Yet, they show no awareness of anything like a papacy or infallible magisterium. The pattern in these passages of referring to sources like past apostolic teaching and scripture without referring to anything like a papacy or infallible magisterium makes more sense under a Protestant paradigm. See my article linked earlier in this paragraph for more details. In addition to the three portions of the New Testament I discuss there (Acts 20, 2 Timothy, 2 Peter), think of the writings of John. He probably wrote in his elderly years, and, like Paul and Peter, he keeps calling on his audience to remember things like apostolic teaching and scripture, but shows no awareness of anything like a papacy or infallible magisterium.
The fact that a few different apostles are addressing these issues in so many contexts is significant. There's a cumulative effect.
It's probably not just a coincidence that so much emphasis on scripture, including the material most cited by Protestants, is found in the documents I'm focused on here (John 14:26, 2 Timothy 3:15-17, 2 Peter 1:20-21, 3:1-2, 3:15-16, Revelation 22:18-19, etc.).
And keep in mind that critics of sola scriptura, like Roman Catholics and Eastern Orthodox, have taken so much initiative to tell us how important it allegedly is to have guidance from an infallible church or Pope, to have a higher form of ecclesiology like what they offer to produce a certain type of unity they claim we should have, etc. They can't tell us how important such things supposedly are, then turn around and say that it isn't problematic for their position when the earliest sources keep bringing up other sources of authority, but don't even mention the Roman bishopric, let alone refer to a papal office, say nothing of looking to an infallible church after the apostles have departed, etc. You could still argue that other factors outweigh this consideration I'm mentioning, but the point I'm making is that it is a consideration that weighs against systems like Roman Catholicism and Eastern Orthodoxy to some extent.