In my opinion: [b]He fought the Vex alone.[/b] This destroyed him. In the time before he vanished he said things that I think should be remembered. These are some of them: [b]No one can open the Vault alone. I opened the Vault [/b](READ THIS PROPERLY: I meaning, alone he opened it). [b]There was no one with me but I was not alone[/b] (referring to the vex). - no where does it say he had others with him. He said it can't be opened alone [i]but he did[/i]. Full VOG Grimoire card description: His name was Kabr. He wasn't my friend but I knew and respected him as a Guardian and a good man. He fought the Vex alone. This destroyed him. In the time before he vanished he said things that I think should be remembered. These are some of them: "In the Vault time frays and a needle moves through it. The needle is the will of Atheon. I do not know the name of the shape that comes after the needle. No one can open the Vault alone. I opened the Vault. There was no one with me but I was not alone. You will meet the Templar in a place that is a time before or after stars. The stars will move around you and mark you and sing to you. They will decide if you are real. I drank of them. It tasted like the sea." That is all I can remember. Pahanin

His Fireteam was wiped from existence. So, by the time Kabr was the only one left, he was alone, but knew he was somehow not alone; he reasoned that it's impossible to get into the Vault alone, so when he entered to Vault, he must not have been alone, even though his comrades had been wiped from time and his memory.

He went in with a team but they were all killed by the gorgons. He was the last one alive and did some magic with the gorgons and made the aegis

At the end he was alone but I believe he did at one point had a fire team one witnessed his death escaped and created the super good advice which he created to talk to him because he was afraid of dying alone after seeing kabr die

He was alone but not alone - his team was wiped from time by the gorgons i believe.