If you miss your dining time, don't have time for dinner in port, are too late for WindJammer, I'd consider these options:
Room Service. $7.95 + 18% gratuity per cabin fee. But that's low per person for 2+ in a cabin. You can order more food that just for the cabin, but I wouldn't stretch it and order for more than 4 people for example (plus that would only increase the wait time). It's also the easiest option, especially after a long port day. You can even get cleaned up while you wait for food. We found the food fine (at least in 2019) - the biggest issues were wait time and temperature.
Sorrento's Pizza. Included. Open late. May have a few sides in addition to pizza. Last cruise their pizza was actually good, way better than pre-2018/2019, when I considered it nearly inedible.
Cafe Promenade. Included. Open 24 hours. Sandwiches and cookies and similar lite fare.
Amber and Oak Pub. Per item fee. Would likely total more than room service, as a burger is ~ $8 for example. Open late.
Solarium Bistro. Included. Seats until 8:30pm per the app for our Ovation Alaska cruise this summer (a bit later than 8:00pm for WindJammer). So this may be the only option for a complimentary sit down dinner after 8pm. Dinner is Mediterranean style buffet with some other made-to-order options (some of which may have an upcharge). Although I'm not sure they'd like you to do made-to-order if you walk in between 8 & 8:30. We really liked their food on our last cruise in 2019 by the way. They are also a great option for a quick breakfast that we found way less crowded than the WindJammer, without sacrificing too many options.
However, after a long active Alaska port day, we tended to just want to grab something quick or get room service, not even go to WindJammer or the MDR assuming we weren't too late, as we just wanted food, a shower, and sleep! So knowing your options and keeping things flexible is a good way to go. I wouldn't try to make arrangements for a different MDR time unless you're sure you'll be up to it.
Also, if you're running late for WindJammer or Solarium Bistro, you could either head straight there from the dock, or send one or two people to drop off backpacks and such at a cabin, and get them a plate of food. You can also take food out of venues, such as if you get there right before they close and don't want to be the last group. Although on late all aboard time Alaska port days, it's common for the WindJammer to be quite full right at closing, due to all the people who miss the MDR.
