Larian Studios Forums Divine Divinity (English) General Divine Divinity. The game addicted.

For the mind controlled soldiers, you can not cure them directly, or get help, but you will meet one of the 3 wizards that cast the spell later in the game, after which they will return to normal, if they are still alive.

There is a second key in the game, that can be used for either Nericon's Garden or the graveyard (see here and here). Once you clear the garden though, and find the treasure there, there is not much reason to return, so the gate doesn't need to be open.