Look at Mickey Mouse, Batman, Spider-Man, Superman & Bug Bunny. All still around after decades of existence. Both Los Angeles and Orlando are getting Super Nintendo World parks. A Mario animated feature coming from Universal\Comcast.
Nintendo will hold the rights to Mario as long as the company exists. Eventually, his original design will enter the public domain while Nintendo still exists just like Disney will still exist while the original design of Mickey Mouse enters the public domain in 2024,
Hard to say. Crazier things have happened as marketing stunts. Look at Coke. They dropped their formula once and the public went in rage mode. They brought it back and have been number one ever since. Although many have said that was their plan all along.