Of course it's not to be taken literally. If such a deal existed along with all the bells and whistles proving a true demon apparition testable with all 5 senses and the deal was legitimate, one would have to ponder the ramifications of such a demon existing with such an offer. If such a ludicrous thing could fully manifest in such a way, one would have to give the afterlife a consideration for being a fact... in which case taking the deal of said demon would be unnecessary anyways.

I suppose if the demon was real, the offer was real, and the afterlife was proven as not existing, taking up the demon on said offer would be something I would personally consider. Notice, I would have some very strict skeptical requirements for proof of the demon, the deal, and nonexistence of said afterlife.... so skeptical in fact that I doubt those requirements could be met.

Regardless any such deal is pointless if the afterlife exists anyways, it would be better to die and experience being more than the psychical self in that event.