So this guy's just some weakling trying to bring back Helvi... for what ends?
Just seems like he was the punching bag for some higher ranking demons and wanted Helvi to avenge him. Why he thought a WAY higher ranking demon would follow what he says is stupid. He assumes a lot of things about Helvi.
Besides, it's not like demons have any shortage of time. She can easily just live a full life with Theo and return after he passes away.