I've always thought the power is capable of holding that dual purpose.  But you're right, when it comes to the massive amount of control and trust that'd have to be established between them before healing is even on the table.

Alright, I think I got more ideas, especially in terms of plot, because I worry about things stagnating if Alexander is just sitting in a locked room for a while, with Lilith having no reason to interact with him much.  Perhaps, not too far down the road, the news that Lilith has captured the bearer breaks out, and the creatures of hell trying to break out assail the fortress in hopes of breaking him out.  It could become a struggle over him as a weapon, and then Xander is in the middle, trying to decide what's in his best interest, both for his life and his morals.

Perhaps Xander [i]has[/i] to escape before he can learn of Lilith's plans and see the benefits of them, and begin to trust her.  That could work.