1, I don't expect most benchys to last longer than people who know what they're for; I imagine the plastic will crumble to microdust before then, but 2. benchys look like little toy tugboats. Society being so destroyed we can't recognize a toy boat while benchys are still around...I'll believe that the last human to hold a benchy in their hands will say "Oh, a weird little toy boat" but not "no one on earth knows what this is or has the start of the beginning of the foggiest clue what it was for."