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.
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.
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.
According to one theory (via Stack Exchange), Gimli did not know about the fall of Moria in The Lord of the Rings: The Fellowship of the Ring movie due, effectively, to poor communication.
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.
Gandalf didn't know that the Mines of Moria had fallen. He mentions he had been through Moria before, but it was before it had been resettled, which means it would not have had the chance to be overrun yet. All that was known about the mines was that the dwarves had gone silent.
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.
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.
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.
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 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.
In the end Tolkien stated that there were probably "at most" seven Balrogs: In the margin my father wrote: 'There should not be supposed more than say 3 or at most 7 ever existed. '
In TA 2941, Gimli was prevented from traveling with his father on the Quest of Erebor because Thorin and Company thought he was too young, though Gimli, being in his sixties, considered himself ripe for adventure and was disappointed to be left behind.
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.
Despite her suspicions of Boromir and the massive rift between the races of Middle-earth, Galadriel understood that uniting all people was the only way they could defeat Sauron. The small act of passing her gift on to Boromir was a step in the right direction that the films failed to elaborate on.
Galadriel: "Do not let your hearts be troubled. Go now and rest for you are weary with sorrow and much toil. Tonight you will sleep in peace." [She whispers to Frodo in his mind, casting her eyes sideways at him.]
In the final minutes, Sauron confesses that he's been manipulating Galadriel since they first met — using her as a way to get back to Middle-earth to fight back against his enemies in the Southlands and indirectly form the land of Mordor but also to get closer to Celebrimbor and the Elven smiths.
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.
