Indiana Jones is a like the James Bond series, there doesn't have to be continuation. They could reboot and bring back the nazis and someone younger to play Indy. They could rewrite the story for the old N64 game Indiana Jones and the Infernal Machine or finish the script for Indiana Jones and the Staff of Kings.
I don't know why they need Ford for Indy anymore. Why can't they do a James Bond or Doctor Who and get another actor to play Indy and reboot the franchise? Odds are it would much better than a guy my dad's age running around fighting Soviets and aliens. Bring back the Nazis as bad guys and put in some one new.