Damage dealt to creatures remains on those creatures until the cleanup step or until an effect removes that damage. If you control Tom Bombadil with at least 4 damage on it as well as a single Saga which has four or more lore counters on it, and that Saga leaves the battlefield later in the turn, Tom Bombadil will be destroyed. This will be true even if that Saga leaves the battlefield as a result of its final chapter ability leaving the stack; state-based actions will be checked before Tom Bombadil's triggered ability could get you another Saga.