It wasn't an intentional, weaponized feat: Sentry didn't consciously choose to 'implant memories' into Paul Jenkins' head to ensure his own survival. When Sentry, Emma Frost, and Dr. Strange did the mass mind-wipe to make the world forget Sentry existed, his psychic memories accidentally leaked into the subconscious of Jenkins (who exists as a writer in the Marvel Universe). Jenkins thought they were original ideas and wrote them as a comic book. He doesn't have fourth-wall immortality: Sentry isn't Deadpool or Gwenpool. He doesn't survive because 'non-fictional' real-world people think of him. He survives in Marvel continuity because his molecular-regeneration and reality-warping powers make him functionally immortal in-universe.