Deleting FB from the App Store will instantly guarantee a trillion-dollar regulatory fine on Apple... that lawsuit will be supported by hundreds of millions of Facebook-addicted users.
Apple knows they can't get rid of FB. It's the largest tech cult in the world today.
It would make for an interesting thought experiment though.
People thought that iOS users wouldn't be able to do without google services either. Today, Apple has replaced google maps with Maps, while google pays Apple $9 billion to keep search default on safari. We have reached a weird inflection point where android may have the larger market share, yet the most lucrative user base use apple products.
I also see what Apple is doing. They are strengthening their ecosystem and making it more sticky, so people have to think twice, maybe thrice before leaving for another platform. And even if Facebook were to leave iOS, where would they go? iOS is still its most lucrative platform, I am willing to bet that Apple would be able to weather the hit in the short run (people are not going to thrash their phones and jump to android overnight and just leave everything else behind), and Facebook just continues to lose money day after day after day.
Meanwhile, Apple can continue to hit Facebook where it hurts - their tracking algorithms and advertising revenue.
If anything, all these events that have been going down the past few weeks just help make the case for Apple to not only continue to strengthen their ecosystem, but to also not shy away from replicating competing services and products where necessary. The best example would be spotify vs Apple Music. I would say that at this point, spotify poses the least threat to Apple because if they do exit the iOS App Store, Apple has a ready substitute for its users.
This way, Apple reduces the risk of finding itself hostage to an influential app. They may not be able to replicate every app in its entirety, but at least enough to offer an interim solution, and this buys Apple time to react accordingly.
Things don't look good for Apple, but I will say that Apple is in a lot less precarious position than the naysayers believe.