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In a dedicated (or "extreme") demonstration of how the phenomenon people today often call "sealioning" is really just a part of the way things must go at times, where I live, the only surefire way to unquestionably be considered dead by authorities is with a body to organically examine. Even if you did what Metro Man did in Mega Mind, it wouldn't typically be followed by a declared conclusion because they have a knack for genetic/bodily testing and making sure no assembly of working organs was able to wander off somewhere. Every status either authorities or laypeople can imbue in you that doesn't follow this mindset will grant you a "probably dead" at best while your living record remains in the back of peoples' minds and filing cabinets.

The absolutely only exception that doesn't merely involve this is to go missing at a certain age, stay missing until you're well over 100, and hope you've actually lived well over 100 so that it counts as "faking" your death (since it's not faking death if you really did die), and though I could try, I would bet my life on the fact I won't live over 100 (which will probably end up being one reason why).