I just watched the episode of Big Bang Theory where Sheldon tells Stewart that the original Robin, Dick Grayson would be next in line to be Batman (in the event that something happens to Bruce Wayne). Stewart then says he’s wrong because Dick Grayson becomes Nightwing, a superhero in his on right. He says it should be the second Robin, Jason Todd.
His reasoning on why Sheldon is wrong makes him wrong also. Because Jason Todd becomes Red Hood.
All that being said, who would be next in line to be Batman if established superheroes aren’t eligible? Also, who would it be if all characters are eligible?