I personally don't believe anything will go worse for the parks. As for Marvel/Star Wars, that's honestly more on Kennedy and Feige who definitely have enough pull and weight to not be talked down by Chapek. And Lucasfilm has obviously seen troubles without him. Marvel is poised for a downturn since Endgame, as it's a battle to get back up. 2020 won't be nearly as big as 2019 for Disney's box office, and coronavirus will effect returns. I get why Iger wants to jump ship, I just think it's bizarre they decided to do it in this fashion.
But I'm not here to discuss conspiracy and hypothetical, because what's the use in being worried over that when all we can see in front of us is pretty much there for the moment. Bring me some meaty, actual news of what Chapek's strings pull in for the company whole and then I'll be convinced. I do think, however, this could be beneficial to the parks. A more savvy leader is what the department needs, hopefully one that can navigate Chapek's eye for budget reduction. (yes, yes, I know you all are scared that a yes man will be plopped in)
I do think that Iger will still have a hand in things for the most part until at least the end of this year. I guess we will see what happens, but the doom and gloom is amusing for sure, especially by parks fans. New boss, same as the old boss.