At the end of it all, this is the key question we are all asking ourselves.
For example: parades have been on their way out for about the past 20 years - when there was a daytime and/or nighttime parade at every park. On the opposite end, years ago only MK & EPCOT really had nighttime shows but they eventually added nighttime shows to both AK & HS. There's a bunch of examples of changes over the years, something goes away and something else come online. This was done over a period of many years - which is much easier to tolerate. Now if you took someone who's last visit to WDW was back in the 1990's and brought them to the WDW in 2019, they would notice a LOT of changes - some they liked and some they may not like and chances are there would be items they remembered they would miss. (I still miss Tapestry of Nations but have gotten over it. Horizons anyone?)
What we are witnessing now could indicate a cosmic shift on park operations and entertainment that will effect how we experience WDW well into the future. It will be similar to what I described above - a LOT of changes. The issue as I see it is that we don't have the fog of time to dull the harsh effects of our new WDW reality. The wounds are too fresh, and there's so many. Entertainment with perceived low ROI has been shown the backdoor, and the parks are practically running on a skeleton crew.
The items that come back first will likely be those that have ROI associate with them - so I would guess character breakfasts are a safe bet. Nighttime shows have to come back, if only to fuel sales for dessert parties. Holiday parties will come back. The items I worry about most would be the ones of the more esoteric nature that could be perceived with low ROI like CoH or CoMS or nighttime games at Boardwalk or the GF orchestra or tons of different little things around the parks and resorts that make WDW what it is to us.
I really don't like even pondering the OP's question or even speculating here because I currently have little hope that most will return, so I'll just offer the following - once I hear that the Electric Water Pageant has started back up I will have hope for the future.