There's a crucial flaw in the premise, honestly. The soul is the price. The entire narrative tension hinges on that trade being absolute. If you figure out a loophole, you've essentially broken the story's contract, and what's left is just a tedious legal argument, not a compelling dark fantasy. The attempts to 'outsmart' the devil in so many webnovels ruin the trope for me. The character gets everything—power, revenge, love—and keeps their soul because of some clever phrasing. It drains all the stakes.
What makes a pact narrative work isn't winning; it's the cost. The slow erosion, the tiny corruptions, the things you sacrifice along the way that aren't in the contract. Your relationships, your empathy, your ability to enjoy simple things. That's where the real 'loss' happens, long before any formal collection. The soul isn't a token; it's the sum of those choices. So you don't 'keep' it intact. You just hope what's left at the end is still worth saving.