Hi Becky, No worries (or as they say in the Lion King, "Hakuna Matata")!
Several of the restaurants will have reservations for Guest's up until closing time (or in your case, slightly past Park closing). In fact, the Grand Gathering Safari Celebration Dinner is held after Park closing (I'm not sure if you are attending this or not). Rest assured that Disney Dining was aware of the Park Hours when they booked your reservation, and transportation for all Resort Guests is guaranteed...so you'll be all set. However, you should know that once you finish eating, the Park will be officially closed, so you'll need to exit without stopping to shop or to go on any other attractions. The bus service will continue up until every Guest has left the Park.
Enjoy your dinner with your group, it sounds like a lot of fun! My family loves the
Tusker House Restaurant, the food is delicious!
Have a wonderful vacation,
Kaylene