Mastodon will not evolve into a single-instance monolith like Twitter because fediverse users are too diverse to agree on a single set of rules. Some instances are general purpose while others focus on specific topics. Some welcome certain types of content while others don't.

If you choose an instance with rules that you agree to follow, you're not likely to be blocked in the first place. But if your Mastodon account is blocked on an instance, it's easy to make a new one on a different instance. There are many other instances to choose from and you can regain your social graph by following everyone again.