Last session, I was DM and the party was engaging an Earth Elemental which was using its Earth Glide to hide in the rocks, pop out and attack and glide away. The party countered, as expected, by taking the Ready action. Specifically, the cleric (higher in initiative) readied Banishment and then the Bard readied Hold Monster with the trigger "when the damn thing pops out of the wall"; both excellent choices.
So, the elemental appears, the trigger is activated, the Cleric acts and succeeds so the Bard is left with no valid target.
My question is, what if the roles were reversed. If the Bard succeeded in holding the elemental, could the Cleric have aborted the Banishment?
Clearly, the Cleric could (should?) have used a different trigger: "if the Bard's spell fails", however, for this question, assume they were both acting on the same trigger.