Here is my opinion. And it's only an opinion. I suspect that the in park dining reservations will come back sometime after the parks reopen but it may take a while. I think that for several reasons. The first is that they may want to get the park reservation system up and running without having the dining reservation system having to interface with it initially. In other words the system won't have to check that you have park reservation to book an in park dining reservation. I also think that Disney is unsure about staffing and other things needed to run a restaurant during this new situation. By not having the pressure of prebooked dining reservations they can adjust dining hours, staffing and other things without having to further cancel reservations. I also wouldn't be surprised if not all sit down restaurants open when the parks reopen.
I would also like to throw out 2 other thoughts. It wouldn't surprise me that initially you won't be able to make attraction reservation times until after you enter the park. Kind of what Universal is currently doing or what they have been doing at the Studios with Rise of the Resistance before all this. I don't think every attraction will need a reservation but the more popular ones will. I kind of look at it as a digital legacy Fastpass deal. Scan your ticket at the turnstiles then book some attractions. With limited capacity it will keep more attraction reservations open for people who are actually in the park at the moment.
Lastly, I have been pondering the word capacity and I think people believe that it's just simple math. Such as a park has a capacity of 60,000 so half is 30,000 and 25 percent is 15,000. I think that Disney is going to look at it differently. How many attractions can we open and under the new guidelines what is the new capacity going to be. Attractions with large queues might have larger availability then smaller queues that can't hold many guests with the social distancing requirements. Also we know there will be less seating, possibly fewer ride vehicles that also may decrease capacity. When you factor in shops that may not reopen, less capacity at food locations you may have a park capacity that Disney is comfortable with that is lower than just a normal 30 percent. Eventually as things shake down you will see Disney adjust and bring back things. But I expect that while they may increase capacity over time, you may see the current reality through August and September. Just my 2 cents.