I can't say I really agree with him on this one. I really would like a Bond-style fate for Indy, with the character living on for future generations to enjoy.
For me as well. And I don’t want to sound unoriginal, but neither is his Han Solo expendable. He IS Han Solo and Indiana Jones, just like Al Pacino is Tony Montana and Michael Corleone, or Sylvester Stallone is Rocky Balboa and John Rambo. Maybe if at the begging they wouldn’t had played these characters, we would be able to see other actors attached to them, but not now after seeing them.
If someone else were to step into the shoes of Indiana Jones, I would basically regard it as an alternative universe. It would literally be a different Indy, unconnected to anything that came before.