They pretty much have no power for the amount of time he has it. And as soon as he relinquishes control, they have it back at full capacity. He's been working on a way to not fully drain the other person but if he could pull it without them losing it, that would be awesome.
Not gonna lie, his power (and probably her) would freak him out. He's pretty big on the dead remaining so, so... yeah. he'd be very civil, but once he knows what she can do, he'd probably not hang around often.