The only single attraction that might cause me to reschedule a whole trip would be Haunted Mansion. Ain't Disney without that.
If the Spaceship Earth extended downtime finally happens and really lasts for over a year, I will be sad to miss it, but will still go during that period. Worth the wait if they actually refurbish it properly, make minimal and well-judged changes (fingers crossed) and remove the screens.
They always leave 2 out of the 3 Mountains functioning, which is sufficient...I don't need to hit the trifecta every visit.
If Flight of Passage were unavailable, I might do a 3-day trip and skip AK (but I might still go anyway). Likewise with Rise at Studios. But as others have said, there's no way I'm ever going to be in Orlando and not parkhop over to Epcot for World Showcase.