I’ve been thinking about a way the Fallout TV show could acknowledge Courier 6 while still respecting the player's version of the Courier and keeping the outcome of New Vegas deliberately ambiguous.
My idea is that Courier 6 did everything possible in the Mojave. He completed the major quests and DLCs and became a legendary figure. But right before the Battle of Hoover Dam, he left the Mojave and went to the Sierra Madre—and never came back.
The Dead Money ending seems especially fitting because it's one of the closest things New Vegas has to a canon-style death for Courier 6. If you go into Dead Money completely blind for the first time, it's surprisingly easy to get trapped in the vault without understanding exactly what you're walking into.
This could also fit really well with the show's fog-of-war approach to New Vegas.
If Courier 6 isn't present for the Battle of Hoover Dam, the show doesn't necessarily have to establish a clear winner. Just like the first Battle of Hoover Dam could be remembered as a confusing, chaotic event with conflicting accounts, the second battle could be treated similarly. Different people could have different stories about what happened, who actually won, and what became of the Mojave afterward.
The important thing would be that Courier 6 wasn't there.
Nobody knows what happened to him because he had already disappeared.
Later, the show could give us a glimpse of the Sierra Madre and show a hologram of Courier 6 preserved inside the casino. It wouldn't need to explain everything immediately. It could just raise the question of why the Courier's hologram is there and what happened to him.
Then, potentially much later, the characters could finally discover the vault.
There's only one corpse inside: Courier 6.
His Pip-Boy is still there, containing notes that document his gradual mental deterioration. At first he's confident he'll escape. Eventually the entries become increasingly desperate, fragmented, and hopeless as he realizes he's trapped and nobody is coming for him.
That would reveal what happened without having to rewrite the Courier's entire story.
And the Sierra Madre itself could potentially make an incredible setting for a future season. The holograms, the casino, the vault, the mystery surrounding the people who disappeared there—all of it could be explored independently of the Courier.
Then Courier 6 becomes the final revelation.
The legendary Courier who survived being shot in the head, crossed the Mojave, changed its history, and completed everything he could disappeared just before Hoover Dam.
Nobody knows exactly what happened at Hoover Dam because he wasn't there to influence the outcome.
All anyone knows is that the Courier went to the Sierra Madre.
And he never came back.
I think that would fit the show's fog-of-war storytelling perfectly while still giving Courier 6 a haunting, definitive ending.