I don't think Mastodon will fail. I like the people I've met here by and large, but I am still extremely concerned by the way defederation can work at the server level as opposed to the user level and it doesn't seem like most think this is a problem. I want to reach the wider world and vice versa without being invisibly prevented from doing so. Maybe this is selfish of me, but if I'm honest that's my use case for social media. I want news and information and discourse and while Mastodon is making strides, if the fediverse is just going to unilaterally cut off a huge part of the world, I will have a choice to make on where to have my main presence.