Although I was looking forward to an endgame DLC I came to the realization that there are just way too many variables and that none of those decisions really affect the endgame besides a few key ones in Fallout 3..
In Fallout 3-v
Let someone else make the sacrifice, use FEV
Let someone else make the sacrifice, don't use FEV
Make the sacrifice yourself, use FEV
Make the sacrifice yourself, Don't use FEV
Have a follower make the sarcifice, use FEV
Have a follower make the sacrifice, don't use FEV
And those changes (Besides the FEV) aren't significant at all, really..
In Fallout New Vegas-v
-If NCR was allied with-
Great Khans were driven out
Great Khans left to support the legion (Meaning they would be destroyed)
BOS was destroyed
BOS were talked into an Alliance with the NCR
You can see where this is going... And this is only ONE of the factions... One variable can mean the absence of hundreds of NPC's.
I think I proved my point