I think we'll have a better idea after Star Wars: Galaxy's Edge ("SW:GE") opens...
I'm one of the people who thinks the crowds aren't going to be as bad as imagined. Disneyland doesn't often close for capacity other than over the Christmas holiday week, and those are pretty short closures. Yes, there's been a random day here-and-there that they've unexpectedly hit capacity, but it's not a normal occurrence.
Why do I believe it won't be capacity-crowded as feared? First, because the most die-hard fans made reservations at the on-site hotels for a guaranteed reservation. Of note, last I checked, there were still on-site rooms available for the night before opening day (that would get you in for opening day). The super fans will have made reservations on 5/2 when they opened the reservations to the public if they couldn't afford an on-site hotel room. Then, you have the fact that people see WDW as a "destination" and Disneyland as a "consolation prize" so to speak. If you can get a "consolation prize" June 24 (the first day without reservations) or wait for the "grand prize" on August something-or-rather, just 2 months later, lots of people are going to hold out for that "grand prize" destination. (Just for clarity, in NO WAY do I believe Disneyland is inferior; quite the opposite actually! But I know several people that see Disneyland in the way described above.) A fair amount of people learned of SW:GE by the commercials on TV, all which say "Reservations may be necessary." Those people that care about seeing it will then look into why/when reservations will be necessary. And anyone who has hopped onto the Disneyland website in the last 3 months has seen a GINORMOUS banner at the top of nearly every screen that SW:GE will require reservations.
Why do I harp on the reservations so much? The casual Star Wars fan isn't going to want to invest all that time/effort into seeing it--on-site rooms, reservations--and will just wait until the hubbub is over, likely later in the summer.
I'm not delusional; crowds will definitely increase! But I don't think it will rise to continual capacity closure levels.
So, if you need to go back to the room for naps, expect that it may take an extra little bit to get back in if you have to wait out a closure. But it's not like you will be unable to get back in for the rest of the night. Also, it's a great plug for DCA
If DL proper is closed, you can head right over to DCA instead!