Hi Daniel!
Thanks for stopping by with the excellent question. I'm happy to discuss!
EPCOT is always one of my favorite destinations, but ringing in the New Year there would make for an even more epic park day. As you can imagine, many guests have the same plan so things can get crowded as the night goes on. I contacted a Cast Member about your question and the short answer is "It depends." Let's walk through a few scenarios.
Though EPCOT has quite a large footprint and capacity-related closures are rare, it's always a possibility. The Cast Member I spoke with indicated that if it got to the point that they were not allowing any guests in, an upcoming
Lightning Lane Single Pass return time would
not guarantee you access. In that case, you would need to speak with a Cast Member on-site to receive a refund for the Lightning Lane purchase.
Date-based tickets don't require reservations, but I also asked about
Annual Passholders who might reserve EPCOT for the day, enter before hopping to another park, and then try to return later. The Cast Member indicated that "there are different levels where we first restrict additional guests before cutting it off." It's a bit of a moving target and your mileage may vary so I recommend staying put in EPCOT if you have your heart set on experiencing an attraction via Lightning Lane Single Pass and any holiday celebrations that day.
I hope this helps you make the best plan for your upcoming visit, Daniel. If we can answer any additional questions please come right back to planDisney and let us know.
Magic and memories,
Amy