Can I ski a full day in Hokkaido and make a flight connection in Tokyo?
Yes, if the connection is the next day. Ski your last day, fly from New Chitose to Tokyo that evening, sleep at or near the airport and fly home the next day. Doing the domestic flight and the international flight on the same day leaves no room for anything to go wrong.
A same-day connection is a bigger risk when the two flights are on separate bookings, which is usual when the domestic leg is with a low-cost airline. You have to collect your ski bags off the domestic flight, take them to the international check-in, check them in again and go through security and passport control. If the domestic flight is late, the international airline does not have to wait for you or rebook you. Check-in for international flights closes well before departure, so the real margin is smaller than the gap between the two flight times. Snow can also delay or cancel flights out of New Chitose in winter.
To keep the last ski day, have your bags packed and ready before you go out. If you're driving to the airport, it's usually fine to keep your bags in the vehicle. They will very likely be safe in Japan. Change after your last run and go straight to New Chitose for an evening flight. There are evening flights to both Narita and Haneda, including low-cost ones to Narita. Low-cost airlines charge extra for checked bags and sports gear, so add that when you compare fares.
Fly into the airport your international flight leaves from, and book a hotel at or close to it. If your flight home is not until the afternoon or evening, you have the next morning free. Near Narita, the town of Narita and its Aeon Mall are a short taxi ride from the airport hotels. Narita is a bit of a ghost town at night, but Haneda has towns nearby, and its in-airport hotels have bars and 24-hour services and onsen.
Another way is to leave the resort a night early and stay in Sapporo, close to the ski areas on the west side of the city such as Sapporo Teine. You can ski there the next day and still be at New Chitose in time for an evening flight.
