Unfortunately, the Fellowship's journey only confirmed what he had feared. Although Gimli knew that Moria could be dangerous in the book, he did not know about Balin's death in The Lord of the Rings: The Fellowship of the Ring movie possibly due to slow communication and Dwarves' perception of time.
Gimli didn't know about Moria's fate because there had been no communication between Erebor and Moria for 25 years, and the Dwarves were hopeful and did not want to accept failure until there was certain news.
He was a descendant of Durin the Deathless, father of the first house of the Dwarven people. Gimli was descended from, but was not a member of the royal line. Through his father, Gimli was also the first cousin once removed of Balin, Lord of Moria, and his brother Dwalin, two more former companions of Bilbo.
Why doesn't Gimli know the password to the Mines of Moria? Gimli didn't know the password to the door because that knowledge was lost. It was too long ago when dwarves had lived there. Elves built the door, back when they were friends with the Dwarves, thousands of years beforehand.
Though Gimli has no children, he is not the last Dwarf of Middle-earth. After the fall of Sauron, his people continued to thrive in the Lonely Mountain. Gimli made his home in Rohan, in the Glittering Caves of Aglarond, and many of his kinsfolk came with him.
Why Didn't Gimli Know About What Happened In Moria? (Khazad-dum) | Lord of the Rings Lore
Is Gimli related to Durin?
Gimli was born in the Ered Luin in the Third Age, son of Glóin. Gimli had wanted to accompany his father on the quest to reclaim Erebor, but at age 62 he was deemed too young. He was a remote descendant of Durin the Deathless, chief of the Seven Fathers of the Dwarves and ancestor of the Longbeards.
There had been no communication from Moria for quite some time, but no one knew exactly what had happened there, or why the colony had gone silent. Gandalf definitely did not know about the Balrog, or even about the orc attacks that had sent Balin and all who were with him to an early grave.
Why didn't he? He had been through Moria (more than once), but if memory serves he had only gone East to West, never West to East. So when he came to this place before, he may not have realized it was a fork in the road as he was coming out if the fork, not into the fork.
By the end of the Third Age, Moria had long been abandoned by the Dwarves, and was a place of evil repute. It was dark, in dangerous disrepair, and in its labyrinths lurked Orcs and the Balrog.
Gimli and the other Dwarves lived in the kingdom of Erebor and, since Erebor was far away from Moria, news would have been slow between the two kingdoms. The journey to Moria was dangerous, so many messengers could have died going to or from there.
Gandalf's occasionally mean attitude towards Pippin is rooted in factors such as the stakes of their mission, Gandalf's protective instincts towards hobbits, and his desire to mentor Pippin, offer him guidance, and see him grow.
Gimli calls Legolas “lad” because the elf is more youthful than him in appearance, if not in actual age. (Note: it is only an educated guess from readers that Legolas is at least 500 years old. Tolkien never specifies his age.)
Gimli is not the last of the dwarves. This is a common misconception because Gimli is the only dwarf who gets a fair amount of coverage in the franchise. Lord of the Rings focuses its narrative primarily on the affairs of men, elves, and hobbits. Dwarves are a secluded race that lives in the mountains.
Balin was distantly related to him, and a descendant of the noble House of Durin. He later went to re-establish the Dwarf presence in Moria, but within five years it was overcome once more by Orcs, and he was killed there along with the rest of his companions.
From TA 2989 to TA 2994, the re-colonization of Moria was an attempted expedition led by Balin to re-take the ancient Dwarven Kingdom of Khazad-dûm. An initial effort was successful in reclaiming some of Moria from the Orcs.
When The Fellowship is taken to Galadriel, she and Boromir have a telepathic conversation which immediately causes Boromir to burst into tears. She senses his desires for the Ring but tells him not to give in because even now, there is hope.
With that option seemingly ruled out, Gimli pushed to descend into the mines of Moria because he believed his dwarfish kindred was still alive. Gandalf, however, was hesitant to take either road. He knew that the Balrog was lurking in Moria, and he also didn't want to face Saruman.
Gandalf's main reason for supporting Thorin's quest in The Hobbit was to eliminate the threat of the dragon Smaug, who would be a powerful ally for Sauron. Despite popular belief, the Balrog known as Durin's Bane was more powerful than Smaug in Middle-earth, being a literal, primordial demon.
The Balrog, like Gandalf, is a Maia. There is a very real possibility that Gandalf will die in this confrontation. As an istar Gandalf is an incarnated maia, and thus subject to all the frailties and fears that Elves and Men are subject to.
When Morgoth's defeat was inevitable, the Balrog fled into the tunnels deep within Middle-earth. They were created by the infamous Nameless Things, and they offered a surefire place to stay hidden. And it did, until the Dwarves delved too deep during the Third Age, disturbing its slumber.
The Hobbit dwarves Óin, Balin and Ori all die prior to The Lord of the Rings, when a colony is sent from Erebor to reclaim the Mines of Moria. Óin is killed by the Watcher in the Water, Balin is shot by an orc, and Ori dies in Balin's Tomb, his corpse featuring briefly in The Fellowship of the Ring.
Did the Dwarves retake Moria after the Balrog died?
There's not a lot of information out there on the details of how the Dwarves reclaimed Khazad-dûm, but it undoubtedly required a lot of Orc-slaying. Without the Balrog, Durin's Bane, Durin VII the Last returned to the Mines of Moria and restored it to the once great kingdom that it was.
However, in the Tolkien novel, Gandalf actually never knew about the Balrog. All he knew was that Moria had been evacuated because of something called Durin's Bane, and that it still lurks inside. And while he does know that Orcs attacked the Dwarven kingdom, it was many years ago, and so he hoped they were gone.
