You can pay for both at the same time. I actually bought and printed my tickets on line so I had them before I got to the park.
As for leaving then coming back, that's what I did. We left around 4-4:30, went home and eat then changed clothes and went back close to 7. I don't think they let you stay in the park but I could be wrong.
You will have to exit the park. Scarowinds is considered a completely separate event for logistical and financial purposes. You can hang out right outside the gates and then re-enter as soon as the park is secure from normal operation. Security will not sweep you out of the parking lot, but they will sweep you outside of the gates- and fast. The goal is to have the park secure from standard operation in 15 minutes. Have a good trip.
