So here is what Groot said.
Spoiler warning: If you still haven’t seen Marvel’s superhero crossover film Avengers: Infinity War, it is recommended that you do not read further if you want to avoid spoilers.
Avengers: Infinity War had one harrowing ending when half of the universe’s life-forms got wiped out. Among these, nearly all the superheroes introduced after phase 1 of Marvel Cinematic Universe also perished. It can be speculated that whether they are really dead or just languishing in another world (like the one inside the Soul Stone), but for the time being, they are gone. Doctor Strange, Spider-Man, Star-Lord, Mantis, T’Challa, they are all gone but the death that was probably the most tragic one was of everybody’s favourite sentient tree, the adorable Groot.
“Groot” has already died before in the first Guardians of the Galaxy, but director James Gunn confirmed that this Groot, previously called Baby Groot and now Adolescent Groot or Teen Groot, is different from the last one, who really died. And sadly, it appears like the second Groot too has departed. Groot can only speak one phrase, “I am Groot” but he can communicate different things through this one single line. Only those who spend considerable time with him can understand what he is saying when he says those words.
So all the Guardians of the Galaxy members could understand the nuances and meaning hidden behind “I am Groot.” Groot said the phrase again just before dying. James Gunn, who worked with the Russo brothers on the film, has revealed what that final “I am Groot” meant. It meant “Dad.” As Rocket was comforting him, Groot called him “Dad” before he was turned into ash.
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“Dad”— James Gunn (@JamesGunn) May 6, 2018
As to his final fate, there are many theories but no concrete answers. It makes sense that Marvel will not kill the second Groot so soon after killing the first one. And we were not over the death of even the first one.
Avengers 4 will have the answer. It will release on May 3, 2018.