What happens to Firefox forks if Firefox dies?

People are right that they'd die. They'd die or be irrelevant or so full of security holes that many sites would block them on principle of protecting their users.

The reason why they might die sooner rather than later with the corporate and (western) government led seizure and lock-down of the open internet is that a company like Google could introduce a slew of new web standards and just completely overwhelm any devs trying to carry on the work of keeping the code alive. They could in other words bury it in a couple years with a mountain of complex new standards and possibly regulations (another thing big companies love doing when they capture the regulatory agencies is use them to keep out the little alternatives by burdening them with things they with their money and huge size can easily bear).

But whether that happens or whether even with security incidents it struggles on for 4-5 years the open web is at that point doomed. It's doomed short of some very large and powerful actor deciding to take up the mantle. Once upon a time the EU might have wanted to do that but all the talk of chat control, all the desire for anti-piracy crackdowns, etc it's not going to be the EU. If I had to make a guess if there is any chance it's that China or some massive Chinese company does it. But I wouldn't count on it. However they're the only ones with anything to gain at all really who might entirely for their own reasons want to create a browser stack entirely free of the west's control and might open source huge chunks of it to the point open source devs could do the rest.

All the forks need to make a common engine independent of Mozilla. Pale Moon did it with Goanna and it is shared between Basilisk and K-Meleon as well. The big problem is that any new engine has to beat being filtered by Cloudflare or other WAFs that discriminate by user agent. A bold idea is for all the Firefox forks to rebase off of the new Ladybird engine and abandon the old Gecko codebase entirely.

Normally I would say community forks have the power to continue the project. However, in this case I think chrome / safari would eventually add enough new features that Firefox forks can't add quick enough. Mozilla at least has some power in pushing the direction of web-standards, which these forks would lack, as well as the larger development team and some corporate usage of the browser which Mozilla has. I also don't see the smaller development community keeping up with security issues found in the browser, particularly pertinent for corporate marketshare and individuals with a stricter threat model (journalists, dissidents, etc.)

The only other factor, is whether Firefox dissapearing would officially create impetus for an anti-trust case against Google. I doubt so under the current American presidency, but I could see the EU being concerned (even if they lack the power the US has to force the company to split). If something were to happen here there would be substantial change in the browser market, but I wouldn't be too hopeful of this happening.

We really need servo to take off...

Most will simply evaporate.

A few will continue to be maintained, but eventually drop off with like one or two slightly stangant active forks.

Well I hope someone takes up the source code and continuea to maintain it

My opinion is there will be a new Firefox, whether using gecko or servo. Hell, I'd start a new foundation myself if required.

Honestly, Firefox would be much better off without Mozilla. A donation model that would fund a small development team that could just focus on making a good browser would work just fine for this.

Hell, all Mozilla need to do is to remove about:config to kill the forks. Due them being Firefox with a user.js (sometimes also a CSS Theme).