Then where does Destruction come in? If we have Ithroen, it's unnecessary, and without him, we can't be sure of our chances. Hell, Drogo will probably take at least one of our high-end combatants with him, seeing how he's a Champion of the Horse God in Shardplate.
And we'd be relying on us being able to defeat all the bloodriders and mooks without getting ourselves killed.
Outside of Drogo, the most dangerous opponents on the field would be the bloodriders. Harlon can kill them with Destruction quickly, if need be. Ideally Ithroen could possess one of them instead of us having to kill all of them, or just have them betray Drogo one by one without us interfering first.
Our men or better yet some of Jorah's First Men can take care of the mooks.
Drogo's initial opponent will be Jorah - the disposable one. He fights defensively until Jon and Robb join battle.
Ideally, we've either got First Men attacking and killing Drogo's horse, or the situation is such that we've managed to get a good distance between them to remove his boosts (it's 100 meters for us and Midnight, so Drogo's boosts may very well have the similar limitations) - maybe have Jorah tell Drogo he found where Dany is, and deliver him into a trap.
Destruction is also there in case the unexpected happens and we get into unplanned combat and need to kill a dangerous foe.