I know they wouldn't do that because it's been marketing gold for them, and just like George Lucas wouldn't kill Han Solo, Disney wouldn't kill Grogu. I think you're right that he'll come back, he'll choose to leave Luke because he's developed too much of an attachment to Din Djarin. It was why Ahsoka didn't want to train him. And they'll use it as another proof that the Jedi Order is inherently bad even though they try to be good.