I won't say how the Dragon Knights died but all I can tell you is that they are now Forgotten.
After their death, and after King Arthur, it was time to bring the old Dragon Knights to help the realm. Nobody can actually explain who or what has resurrected them but this may be solved if we bring back the story to the end.
When they got resurrected, they had no equipment, nothing at all. The dragon knights, now known as Forgotten Dragon Knights, were resurrected but have got their power and strength reduced. May it be Gods who decided to do all of that? They all had to start over but they remember who they are and what happened when they were Dragon Knights.
Back to life, in a new world of Hibernia, they are a little bit lost. The forces who resurrected the Dragon Knights have regrouped them together to form a guild called "Forgotten Dragon Knights". Being a small guild, they have to explore and recruit new members to join it.
The dragon armors and weapons now belong to lots more people... not only on Hibernia but Albion and Midgard too. The situation is critical. Now, they don't have advantage on their enemies and can die more easily.
If some old forces find out that the dragon knights are back and find their location, they can have serious troubles. Let's grow up and prepare for any eventual attacks! Keep up the good strategies and fight with honor of serving Hibernia again!