To me, the only thing that is NOT okay is archiving entire videos or segments of such. Memes, animations, and out of context videos/compilations are okay. If your archive is a video taken out of any part of their videos and it clearly tells a sequence of events with no cliffhangers or missing context, imo it should not be allowed as it goes against the spirit of the channel. However, if your archive evokes memories (eg. the disclaimer song, Mark's eboy TikTok, or a complete list of the titles of their videos) without telling exactly what happened with context in the form of video, it is allowed as it is what Mark and Ethan want - to enjoy the memories of the channel. I feel that reuploading their videos on other platforms is dishonest; it feels like trolling or mugging.
An excuse some people like to give is that they have barely started to watch the videos when the channel ended. Well, I was one of those people; I only joined 15 days before it ended. But I made the most of it. Even if you had only one day, even if you had only one hour left, you might as well have watched some of their videos, take a small peek into the life of Unus Annus. And I did acknowledge that I made the mistake of not joining them earlier when I had the chance to. And I do regret it. But I still feel that my time with them was fruitful, but in a weird, different, and indescribable way.
And despite the fact that I may never understand the people who never even got to witness the last day, my advice for them is: ask around. Let people impart the legacy of Unus Annus on you. It may seem pointless at first, but it is a selfless act that your friends, and probably even you, will appreciate. They will get to cherish the memories of the good times they once had, and you will get to experience the life of two people, not as a memory, but as a pure legacy. And if I had the chance to look on someone else's life as a legacy, I would. I could only imagine how magical it must feel, to think that, yes, that was undeniably real, and I am only experiencing it after it all ended.
Woops, got carried away. Anyways, imo replacing entire videos is just plain wrong, and there are so many other, better ways to enjoy what is left.