Hi Younique, and welcome to cruise-chat.
When you say you won't be dining on the ship the day you're in Nassau, are you referring to skipping dinner only, or breakfast and lunch, as well? The reason I ask is that the waiters work these meals too, even at the buffet, so I would keep that in mind.
But, I can also read your question a second way...and that is whether the ship's dining is open on a port day. Please be assured that it is. They might close the dining room for lunch, but a buffet will be available.