I've been twice, during a late February OKW stay, once for lunch and once for dinner. Both times, the place was less than half-full.
It always pays to call ahead when you decide you want to go, even just 15 minutes before, just in case. But, I wouldn't sweat it much.
Even when we stay at OKW, we don't necessarily go there often. We might just as soon order in and eat in the villa, or we might take the boat to DTD for dinner.