The Perfect Plan to Avoid the Death Ending

"I am Herreith Eckbert. You are the one who woke me up."
"...Sorry? Who are you again?"
"Pleased to meet you, Master."

I accidentally ended up unsealing a demon. And to top it off, I got tricked into a fraudulent contract?

"This contract remains valid until your death."
"...Excuse me?"
"It's a lifetime contract, my naïve young lady."
"...But I'm terminally ill."

His blue eyes wavered in shock. At this point, I'm not sure who's really been scammed here.

(Source: Feelyeon Management, translated)