Honestly I doubt Marvel is that screwed. Getting Xmen and FF probably means they have more potential IP's than they could possibly use in the near future. They will no doubt have to tweak some F their plans moving foreward, but in the grand scheme of things I doubt losing Gunn will matter that much.
The public learned the Director of one of Disney's biggest film franchise and brands aimed at families and kids made Rape and Pedophilia including a "joke" involving the Giving Tree and a child. Groot was jokingly called the Giving Tree in Guardians it's naive at best to think this was going to just blow over. Pedophilia has a unique stigma in society and add Hollywood, Family Property, Marvel, Disney, and Politics this was every Clickbaiters dream it wasn't going away and Disney knew it. As much as people want to believe this decision has hurt Disney truth is headlines reading "Disney faces criticism for firing Director over old offensive tweets" are better than "Disney keeps Director who made Rape and Pedophile Jokes"
I don't like what happened to Gunn and I despise the people who caused it but I'm also a realist and understand why Disney did it and know that Marvel Studios will be fine even if the worst cast scenario happens and Guardians 3 doesn't happen especially since Guardians 2 was a nice bow on most of their story arcs.
Disney will probably omit all of Drax's screen time in Avengers 4. He will end up being one of the permanent heroes never to return because he kept on defending Gunn.
I've seen you state this several times over the last few pages. it's worth pointing out, I think, that advertisers, stock holders, and share holders don't make business decisions for Disney or any other corporation, and are not consulted about them. Board members might be (but in this case they weren't). It's also remotely possible that sizeable investors in a specific movie might have some input, but it's unlikely that would happen at the level of the Gunn situation.
This is known to be the decision of one man, Mr. Horn, who quite intentionally released a statement about his decision in a specific manner that absolutely meant Disney could not override it without firing Horn first.
The supposition that Disney did the best they could because only Disney knows the whole story is, to put it simply, unsupportable and frankly silly.