Firefox is already on life support. Ending it would be an act of mercy at this point.
So long as someone still has the source code for the latest build somewhere on the internet, and that code builds into a working executable, Firefox still lives. It's all of the other crap that dies, the crap that no one asked for.
FF needs to be run like the group handling the Linux kernel or the Python Software Foundation. There's a BDFL or a trusted group handling the general direction of the project, and volunteers who give their time to develop the code. Occasionally there are sponsors who throw a few bucks the way of the volunteers so more concrete efforts can occur.
No. Without funding, the rendering engine would quickly fall behind, and the browser would become nothing more than another Chromium reskin. I hope you like a Chrome/Safari duopoly, because that's what you are effectively advocating for.
It won't be as easy, but the experiment of "let's drive value creation with free and open source software!", at least how Mozilla has done it, has failed.
We won't be able to keep up with the pace of changes Google makes to the "living standard". That was one of the intended side effects of making web browser behavior into a "living standard".