one of many scenarios supporting Shanks would die:
Ace is dead. Ace was Luffy's role model and someone really important to him. Blackbeard took him away. Shanks is also Luffy's role model, Luffy even nicknamed himself Strawhat Luffy because his ambition to return the hat when he surpass the original owner. The two were quite similar in their relationship to Luffy, and furthermore there was some kind of grudge between Shanks and BB, seeing Shanks' scarface. BB may be the cause of Shanks' death the same way he caused Ace's death, because there's something BB wanted (secrets of Raftel who Shanks possibly knows when he was a rookie? etc). I'm not saying BB himself will kill Shanks, not necessarily directly. But like in Ace's situation, he might be one of the core reason of Shanks' death. I want Kong to kill Shanks, btw. That oldie seemed legendarily haxxed.
One of many alternative scenarios supporting Shanks would live:
Like my previous statement of the possibility, Luffy even nicknamed himself Strawhat Luffy because his ambition to return the hat when he surpass the original owner. It's like he was the reason for Luffy's dream to become PK. So quite possibly also, Shanks would become some kind of secret boss after Luffy beat BB in a fight / war that engulfs and determines the fate of the world. He would be deemed Pirate King at that time, but he then must fulfill his promise to Shanks by returning the hat, by and after beating him of course.