Awesome, we played it right, it turned out it didn't matter since I had another Isaiah in my hand.
A related question, lets say I was in a slightly different situation, let's say instead of the 2011 Isaiah, I had the prophets Isaiah, and in my hand I had a Valley of Salt in my hand, can I choose the instead and then play Valley of Salt?
Valley of Salt (RA2)
Type: Hero Enh. • Brigade: Purple • Ability: X / 2 • Class: None • Special Ability: Interrupt the battle and discard up to X Evil Characters. Opponent may place them beneath deck instead. Cannot be negated if used by King Amaziah.