It won't happen. The 'main' question about the issue, Firing mods and forced relicensing: is Stack Exchange still interested in cooperating with the community?, has been viewed 124,000 times (at the time I'm writing this) in three weeks. That's a lot, but it's just a tiny fraction of the 10 million visits to Stack Overflow every day. The traffic to that question is comparable to a site like Code Golf. Not the smallest site in the network, and if they decide to leave they will be missed, but it will hardly make a difference to the network.

(The Official FAQ on gender pronouns and Code of Conduct changes has 110,000 views, mainly because it's featured across the network, but it could very well be that a typical Stack Overflow user sees a heavily downvoted post, is not interested in the topic and quickly closes their browser tab. And it's still much lower than typical Stack Overflow traffic.)

Bottom line: the vast majority of the users have absolutely no clue about what's going on. They come here to ask their programming questions or answer a few, not to hear about the troubles of the vocal minorities (however important they are).

Feel free to leave, develop and run something yourself. If enough people go with you, you may be able to rebuild a community. But you're forgetting two major things here:

Cost and effort.

Somebody is going to have to pay for that, and somebody is going to have to put forward the effort. Building a community isn't easy. Rebuilding one isn't either. The number of people interested in your idea might be substantial (yet not even close to a relevant enough minority), but even if you'd get a hundred or so interested: how many of those are willing to pay for it?

We got something fairly unique with the SE network and that makes it hard to find an alternative. I'm not convinced you can deliver an alternative either. SE has momentum, and it's going to take a bigger dumpster fire than the current one (and all previous ones) to halt that. Which means not only will you have to rebuild a community, you'd facing fierce competition while doing it.

Stack Exchange can't keep the community from leaving.

If the community wants to leave, Stack Exchange, Inc cannot keep it from doing so. It can only hope to negotiate more favorable terms. There already has been talk here and on other sites of starting a new service seeded with the questions and answers from the sites here. The proposed spinoff would be better for both parties than a competing service.

How about just a step in that direction?

SE could disengage somewhat, & devolve control to the communities on each site: of administrative tasks such as merging accounts, adding question close reasons, arranging elections; & of deciding on & enforcing standards of acceptable behaviour. Rest content with being a host & a service provider, without trying to micro-manage. If any site becomes a positive embarrassment, warn the community once or twice, then shut it if they can't or won't fix the problem.

The immediate benefit to the company would be that they wouldn't need to employ nine Community Managers (& a Director of Public Q&A & a Director of New Community Development)—which must cost them well over 500k$ a year—, while still receiving revenue from advertising. And relations with the communities might well improve with a little more distance & a clearer demarcation of responsibilities.

It may be time or it may not be time, nobody knows really until it happens. Anyway it would have to a competitor if the company doesn't just donate the software and domain names, which I think is unlikely. But experience tells us that market leaders seldomly stay in that position forever.

Some general thoughts:

• The activity on the network is in slow decline in number of questions, answers and views of new contributions since a few years. It's not just StackOvefflow. This trend might continue.
• The signal to noise ratio might decrease further with the missing emphasis on quality, reducing the overall usefulness.
• Progress in technology might make it easier to clone the platform technically in the future.
• There might be a tipping point in user migration. At some point migration might accelerate.
• StackOverflow needed around one year of growth to be established back then in 2009.
• A competitor would not start at zero with the content but rather on kind of equal height. The license of the content is unfortunately unclear currently.
• A clear vision where a competitor would be different from the current SO model would probably be helpful.

It must sound like a very otherworldly thing to say - Stack Exchange losing its momentum, fire, and even going down the pits, but do not fool yourself by thinking just because the number of people potentially leaving this site due to their issues with the current affair of events, being less than 1%, will not change a thing.

Everything's going to change.

The world as we know it is controlled by far less than 1% of Earth's total population. Look how that's been going. We have a system, and you can't lift a finger (everything's governed by money). If those people lifted their hands in the air and said "we've had enough", no system will exist.

Stack Exchange isn't a deity. It's your every-day company across the street that shares its success thanks to its users, and most importantly - the ones who're so intoxicated into their amazing idea, that they'd be willing to expand it into the tangible reality as part of their own volition. Those people are the moderators. Those people, who crave to add their community to Stack Exchange, and like agents try to push it to the very top, promoting all those "beta" label requirements to their peers, because they need them to be fulfilled. They are the driving force. Infected by this ideal, they make their way along the ladder, gaining new permissions, making them feel even more special, until they reach the pillar.

What pillar? The company's governed by its products - the users. They simply have to turn their original idea into multiple profitable ones, and you get a thriving self-driven business.

We're all here because we're good people. We want to help others. We want to build a repository of all possible questions and answers - a great idea. But you need to realize that every effort you pour out of your soul, you pour into the bowls of this company. And as a company, they profit out of you.

If you as a person, even for a second believe you've been abused, especially if you're the one that made this site become what it is - simply stop being their patriot. There are tons of other companies out there who'd welcome you in with open arms, and even bargain with you just to use them.

Often the biggest things in our world, are the most fragile.

Both yes and no

I think there are two different issues at play here, firstly StackOverflow. This site is too big to move its community overnight. I live in hope that one day there will be a better option than SE for that particular community but in many ways it's the least affected by recent changes, I think ultimately its size will sustain it for many years to come.

The smaller sites are a different matter entirely, IMO a number of them are no longer viable (cf religious sites + life advice site such as parenting). I think it's likely that large sections of those communities will move elsewhere or disengage completely. Its sites like this that would benefit immediately from a similar to SE alternative.