As I understand it, if he dies, he would go to Soul society. So that would be immortality right there. Bleach has this spirit concept of interconnectedness, with the important distinction of your moral alignment determining where your spirit goes and what becomes. There is no concept in Bleach of "nothingness," even from the hollow that are defeated.
If your question was, can he ever be defeated…probably. Just unlikely, because he's worth a lot of money to the writers alive. That is his best protection.