Bunch of companies get a lot of their customers through Facebok. Those will probably support (finanically and otherwise) FB as long as there are no obviously better ways to get customers. Not for any sentimental reason, just because their business relies on it.

Not necessarily. Businesses are usually fine with making things worse for themselves if it also impacts all of their competitors, preferably even more. That is, as long as a business comes out a bit more ahead of their competitors, a business is usually just fine with making something worse for everybody.

So, even if a business currently gets a lot of revenue from Facebook, as long as a business thinks that other businesses in their field are more dependent on Facebook than they themselves are, they should be fine with Facebook declining.

They have two major things.

1. Money

2. The fact that they are the only source of information that a good percentage of the world uses.

Money can be used to buy power, and they already have a not-insignificant level of control over the flow of information (which is power itself).

Facebook's ability to prop itself up and exist as it does, despite all the animus against it, reminds me of the essay Meditations on Moloch.

Still, absent an adequate replacement people will continue to stay there.