I don't think luffy will or should die by the end of the series. It is a realistic outcome but based on a few other characters I don't think that should happen. Before roger became the pirate king he actually had a good run of 30 years of being a pirate. It took him that long to turn himself into a legend which has inspired an age of piracy. WB, who was essentially a second pirate king and the most powerful pirate until the moment he died, had a long run of roughly 50 years as a pirate. Before the timeskip luffy traveled the first half of the grand line for a period in between 6 and 12 months. If the second half of the series takes place in a similar period of time then luffy's actual pirate career would have lasted in between 1 and 2 years. Even if luffy becomes pirate king (even though it took roger 30 years to do it and WB's 50 year run left him kinda a step short of that) in such a short period of time it would make little sense for his career to end so soon. Even if luffy does make it all the way through the GL it does not mean the GL will no longer hold no secrets for him. The first half still has 6 routes which he has yet to explore and there will still be many places in the NW to explore once he is done crossing it. I don't think it would make sense for luffy's career to end as he makes it all the way through the GL.
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