Uninstalling 8 Ball Pool will not cause you to lose your current league or any progress, provided that your account is properly linked to a social media account (like Facebook or Google). If you have a guest account and uninstall the game, you will lose all progress, including your league status, as guest accounts do not save data in the cloud15.
To ensure your progress is retained:
: Make sure your game is connected to a social media account before uninstalling.
: If cloud saving is enabled, all your game data should remain intact even after uninstallation3.
If you follow these steps, you should be able to uninstall and reinstall the game without losing your league or other progress.