Only Governors in the alliance at the moment the matchmaking phase starts (23:00 UTC on Sunday) can be ranked on the leaderboard. If you switch alliances midway, your points will be retained. Returning to the original alliance from the start of matchmaking allows you to continue earning points. However, points earned in other alliances during the event won't count towards your original alliance's points, and won't be included in the leaderboard after returning to the original alliance.