1) Even if Oculus lose and Facebook have to fork out the entire $4bn (they may lose but there's a good chance that they'll win anyway imo, and it's VERY doubtful that they'll have to fork out the maximum amount of cash in this cash grab, again, imo) it won't affect the running of Oculus in the slightest. $4bn isn't a great deal of money for Facebook (which in itself is a bit frightening tbh) and Zenimax haven't demanded that Oculus stop selling the Rift or that Oculus stop producing content for the Rift or that Oculus stop selling Oculus Rift content for the Rift. Like I've said, it's a blatant cash grab.
2) This won't affect Carmack in any way. The man is a legend in the industry and won't have any problem getting a job ANYWHERE he wants.
3) I doubt that Carmack will leave Oculus after this, even if Zenimax win the case
4) Unfortunately a good chunk of whatever settlement they get should they win will go to their lawyers plus the upper management of Zenimax. You'll see some going towards development for various projects but don't expect them put put too much towards that because, well, lawyers and upper management (who also happen to be lawyers I think..? I could be wrong but I'm sure I saw someone on this thread mentioning that).
What I'm not sure about is what happens if Zenimax loses this case and Oculus win..? Do the Oculus lawyers put in a counter claim for costs, compensation and damages..? No idea how these things work. If they do then that means that, in theory, Oculus can counter-claim $4bn, can't they..?
$4bn is what Zuckerberg probably has down the back of his sofa, but how much cash reserves does Zenimax have..?
As much as I LOVE the Elder Scrolls and Fallout franchises I hope that Zenimax lose this case, and lose a good chunk of change in the process. The Zenimax upper management had the chance to invest in this early on in terms of both time and money and they didn't bother. And now they're sore about it. They don't deserve a damned thing from Oculus, particularly considering the disrespect they showed Oculus during that now infamous meeting where they called the Oculus upper management staff 'kids' and demanded a ridiculous 15% stake.