Has any law ever passed, signed and adopted based on the possibility that something might happen?

Maybe I'm missing something, but you seem to describe a lot of laws.  For example, the 25th Amendment to the Constitution addresses the situation where a President becomes temporarily unable to serve.  The law regarding presidential succession addresses a situation where either the President and Vice-President become incapacitated simultaneously, or the President dies when no Vice-President is in office.  The War Powers Act deals with the authority of the Commander in Chief in various hypothetical scenarios.  There are laws on the books regarding evacuations and authority in the even of various hypothetical disasters, natural and otherwise.  Not an unusual situation.