Considered a legend among the Marines, Garp is certainly an important character in One Piece, even though Eiichiro Oda never paid much attention to him. However, things were different in the final story.
When the story finally begins, Koby has been captured by the Blackbeard pirates, leading Garp to rescue his student. However, entering enemy territory alone, without major support from the Navy, was a risky move.
Garp is dead?
When he arrived at Blackbeard's territory, Garp alone faced all the pirates in Blackbeard's crew. He demonstrated the strength of someone who once rivaled the Pirate King Gol D. Roger. However, Garp was tricked in battle and had a sword pierced through his body. Additionally, former Admiral Kuzan stabbed Garp in the chest with a giant icicle. Garp was then frozen and One Piece no longer mentioned him.
After so many fatal injuries, as well as allegedly freezing to death, fans naturally wondered if Garp was dead or not? There's a good chance he's still alive. The reason is simple: Blackbeard is not on the island and with all his evil plans, he may want to use Garp in some way against the Marines, which Oda himself has hinted at this is what will happen.
Blackbeard can negotiate Garp with the Government
In addition to his strength, Blackbeard is also known for his cunning, as evidenced in his plan to hand Ace over to the World Government and infiltrate Impel Down. Blackbeard also attempted to negotiate Koby with the World Government, demanding official nationhood for his pirate island. Kuzan clarifies that this is impossible, as Koby is an agent of SWORD, an organization with no ties to the World Government.
However, the story takes a completely different turn when Blackbeard has Garp in his hands, because he is a Marine Hero, respected by all marines in the world. A legend who saved the world from the strongest pirates in history. Garp fits into Blackbeard's plans and so the Government may be willing to negotiate.
Garp's role in the final story
Garp is a valuable piece in Blackbeard's game, as he can be used for his former desire to turn the pirate island into a full-fledged nation. It's hard to imagine what this story would be like. Blackbeard wouldn't have stood a chance against Garp, Sengoku, Tsuru and the rest of the Marines, as well as the members of the World Government.
Using Garp would mean starting a major war with no chance of winning, which Blackbeard has repeatedly made clear that he prefers to avoid battles, most recently his confrontation with Rayleigh. Blackbeard would probably give up this fight knowing the tide of battle could turn against him.
In this hypothetical scenario, Garp would be rescued to take on a more important role: fighting the World Government. Garp always expressed contempt for the Heavenly Dragons due to their inexcusable brutality, which is why he never rose to the rank of admiral, as he would have had to serve them. With Vegapunk's message pushing the World Government as enemies of humanity, the navy itself may rebel, with Garp himself leading the revolution and facing the Heavenly Dragons.
