the most basic way is to set a 'flag'.
OnClick & LevelCompleteDialogFlag = 0 (for your gameplay click event)
OnClick & LevelCompleteDialogFlag = 1 (for your End Dialogue click)
then just set the flag to 1 when the level is over and it will allow that click to happen and NOT the gameplay click event. Just remember to re-init it to 0 so your gameplay works correctly when you go back into to playing..