Sure! Just let your servers know that you won't be dining. You might give them a heads up the evening before.
Alternatively, if you feel okay about it, our daughter ate in the MDR without us, joining our table mates for dinner when we went to Palo on two different cruises. She was 7 the first time and 8 the second time. Our servers took great care of her!
Both times it was later in the cruise and she had made friends with the other little girls at our table and we spoke with the other families and made sure it was cool with them before we did it. In both cases, they were fine with it. We had also made friends with another family on board that had invited my DD to join them as well on one of the cruises.
There are a lot of options, but in short, it's no problem for you to chill in the MDR without eating.