It's based off GNU Social, which is based off Ostatus. It uses an email like identifier. The term 'server' in this case is really domain. You are correct about loosing that identity if the server goes away, but that is pretty much the case with anything you don't directly control. GNU social has a single user mode for this very reason.

"that is pretty much the case with anything you don't directly control."

I disagree, you can own a DNS domain and change mail provider, bringing your identity and domain along.

Also, it's not because other services do it that it's a good thing!

This question occurred to me while reading the article. Thanks for pointing this out. This seems like a serious limitation. Is the solution just for everyone to run their own instances?

It's really exactly like email, though. If you're currently user@gmail.com but you want to switch to user@outlook.com, you'll have to notify all your contacts to start using your new address. At least in Mastodon you can update your @user@instance-a profile to say that you've now moved to @user@instance-b so that your followers know where to find you.

It's exactly like email if you use gmail or yahoo. So... WHAT'S THE POINT? Whynot use twitter then?

With email, you can use gmail, or yahoo, or buy a domain and host it yourself, or pay a provider (including google) to host your domain.

Are there options to host your domain on Mastodon without hosting it yourself?

Also, what are the chances that the current servers/providers will still be around in 2 or 5 years?

Yes, there's for-pay Mastodon hosting.

As for why not Twitter: suppose you want a private instance for your family. Or company. Or softball team. Mastodon makes it trivially easy to launch an invitation-only server so that you can chat and share images with just those people.

It also means that you and I can host instances with different community standards. Maybe you want to focus on liberal horse-lovers while I want a hangout for Republican fisherman. Mastodon lets us both go our own way, and gives us tools to decide whether our very different servers should even talk to each other.

As others have replied/posted, the concept is not unlike email. And considering the billions of people who use email - and many who at least numerous times in their lifetime have switched email addresses - this hasn't stopped adoption of email over time, right?

Yes

That seems like a major obstacle to mass adoption. The average HNer will understand that, and be willing and able to do it, but the average person will not.

Not quite. The average person will likely not care too much about their identity being bound to a particular server (if they're aware of it at all), especially as many large and stable instances are available for guests to register and use.